Implantable medical device having flat electrolytic capacitor with tailored anode layers

ABSTRACT

Flat electrolytic capacitors and methods of making and using same in implantable medical devices (IMDs) are disclosed, the capacitors having a plurality of capacitor layers of an electrode stack formed of tailored numbers of anode and cathode layers to fill the available stack height space in the capacitor case. The capacitor is formed with a capacitor or electrode stack assembly having a stack assembly thickness or height H N  that is tailored to fit a case wall height H cw  of the capacitor case with minimal wasted space and allowance for any stack height tolerance t o . The electrode stack assembly comprises a plurality of N stacked capacitor layers each having a specified capacitor layer thickness or height. At least N 1  capacitor layers have a first capacitor layer thickness T 1  and N 2  capacitor layers have a second capacitor layer thickness T 2  where N=(N 1 +N 2 ), and H N =N 1 *T 1 +T 1 *N 2 . The N capacitor layers are preferably formed of a cathode layer, and anode sub-assembly and at least one separator layer comprising one or more separator sheet on either side of the cathode layer and the anode-layer sub-assembly. The anode sub-assemblies of the N 1  capacitor layers comprising x anode layers each having anode layer thickness t x  stacked together, each anode layer having an anode layer thickness T x . The anode sub-assemblies of the N 2  capacitor layers comprising y anode layers each having anode layer thickness t y  stacked together, each anode layer having an anode layer thickness T y .

RELATED APPLICATION

[0001] This application claims priority and other benefits from U.S.Provisional Patent Application Serial No. 60/080,564, filed Apr. 3,1998, entitled FLAT ALUMINUM ELECTROLYTIC CAPACITOR.

[0002] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/103,843 filed Jun. 24, 1998 in the names of MarkD. Breyen et al. and entitled IMPLANTABLE MEDICAL DEVICE HAVING A FLATELECTROLYTIC CAPACITOR WITH LIQUID ELECTROLYTE FILL TUBE.

FIELD OF THE INVENTION

[0003] This invention relates to implantable medical devices (IMDs) andtheir various components, including flat electrolytic capacitors forsame, and methods of making and using same, particularly to an electrodestack assembly having a plurality of capacitor layers formed of tailorednumbers of anode layers of selected capacitor layers to tailor the stackassembly height to fill the available stack height space in thecapacitor case.

BACKGROUND OF THE INVENTION

[0004] As described in the above-referenced parent patent applicationSer. No. 09/103,843, and the provisional application that it claimspriority from, a wide variety of IMDs are known in the art. Ofparticular interest are implantable cardioverter-defibrillators (ICDs)that deliver relatively high energy cardioversion and/or defibrillationshocks to a patient's heart when a malignant tachyarrhythmia isdetected. Current ICDs typically possess single or dual chamber pacingcapabilities for treating specified chronic or episodic atrial and/orventricular bradycardia and tachycardia and were referred to previouslyas pacemaker/cardioverter/defibrillators (PCDs). Earlier developedautomatic implantable defibrillators (AIDs) did not have cardioversionor pacing capabilities. For purposes of the present invention ICDs areunderstood to encompass all such IMDs having at least high voltagecardioversion and/or defibrillation capabilities.

[0005] Generally speaking, it is necessary to employ a DC-DC converterwithin an ICD implantable pulse generator (IPG) to convert electricalenergy from a low voltage, low current, electrochemical cell or batteryenclosed within the IPG housing to a high voltage energy level stored inone or more high energy storage capacitor, as shown for example, incommonly assigned U.S. Pat. No. 4,548,209. The conversion is effectedupon confirmation of a tachyarrhythmia by a DC-DC “flyback” converterwhich includes a transformer having a primary winding in series with thebattery and a secondary winding in series with the high energycapacitor(s) and an interrupting circuit or switch in series with theprimary coil and battery that is periodically opened and closed during acharging cycle. Charging of the high energy capacitor is accomplished byinducing a voltage in the primary winding of the transformer creating amagnetic field in the secondary winding when the switch is closed. Thefield collapses when the current in the primary winding is interruptedby opening the switch, and the collapsing field develops a current inthe secondary winding which is applied to the high energy capacitor tocharge it. The repeated interruption of the supply current charges thehigh energy capacitor to a desired level of several hundred volts over acharging time of the charge cycle. Then, the energy is rapidlydischarged from the high voltage capacitor(s) throughcardioversion/defibrillation electrodes coupled to the IPG through ICDleads and arranged about or in a heart chamber or vessel if thetachyarrhythmia is confirmed as continuing at the end of the chargetime. The cardioversion/defibrillation shocks effected by discharge ofsuch capacitors are typically in the range of about 25 to 40 Joules. Theprocess of delivering cardioversion/defibrillation shocks in this waymay be repeated if an earlier delivered cardioversion/defibrillationshock does not convert the tachyarrhythmia to a normal heart rhythm.

[0006] Energy, volume, thickness and mass are critical features in thedesign of ICD pulse generators that are coupled to the ICD leads. Thebattery(s) and high voltage capacitor(s) used to provide and accumulatethe energy required for the cardioversion/defibrillation shocks havehistorically been relatively bulky and expensive. Presently, ICD IPGstypically have a volume of about 40 to about 60 cc, a thickness of about13 mm to about 16 mm and a mass of approximately 100 grams.

[0007] It is desirable to reduce the volume, thickness and mass of suchcapacitors and ICD IPGs without reducing deliverable energy. Doing so isbeneficial to patient comfort and minimizes complications due to erosionof tissue around the ICD IPG. Reductions in size of the capacitors mayalso allow for the balanced addition of volume to the battery, therebyincreasing longevity of the ICD IPG, or balanced addition of newcomponents, thereby adding functionality to the ICD IPG. It is alsodesirable to provide such ICD IPGs at low cost while retaining thehighest level of performance. At the same time, reliability of thecapacitors cannot be compromised.

[0008] Various types of flat and spiral-wound capacitors are known inthe art, some examples of which are described as follows and/or may befound in the patents listed in Table 1 of the above-referenced parentpatent application Ser. No. 09/103,843.

[0009] Prior art high voltage electrolytic capacitors used in ICDs havetwo or more anode and cathode layers (or “electrodes”) and operate atroom or body temperature. Typically, the capacitor is formed with acapacitor case enclosing an etched aluminum foil anode, an aluminum foilor film cathode, and a Kraft paper or fabric gauze spacer or separatorimpregnated with a solvent based liquid electrolyte interposedtherebetween. A layer of aluminum oxide that functions as a dielectriclayer is formed on the etched aluminum anode, preferably during passageof electrical current through the anode. The electrolyte comprises anion producing salt that is dissolved in a solvent and provides ionicelectrical conductivity between the cathode and the aluminum oxidedielectric. The energy of the capacitor is stored in the electrostaticfield generated by opposing electrical charges separated by the aluminumoxide layer disposed on the surface of the anode and is proportional tothe surface area of the aluminum anode. Thus, to minimize the overallvolume of the capacitor one must maximize anode surface area per unitvolume without increasing the capacitor's overall (i.e., external)dimensions. The separator material, anode and cathode layer terminals,internal packaging, electrical interconnections, and alignment featuresand cathode material further increase the thickness and volume of acapacitor. Consequently, these and other components in a capacitor andthe desired capacitance limit the extent to which its physicaldimensions may be reduced.

[0010] Some ICD IPG employ commercial photoflash capacitors similar tothose described by Troup in “Implantable Cardioverters andDefibrillators,” Current Problems in Cardiology, Volume XIV, Number 12,December 1989, Year Book Medical Publishers, Chicago, and as describedin U.S. Pat. No. 4,254,775. The electrodes or anode and cathodes arewound into anode and cathode layers separated by separator layers of thespiral. Anode layers employed in such photoflash capacitors typicallycomprise one or two sheets of a high purity (99.99%), porous, highlyetched, anodized aluminum foil. Cathode layers in such capacitors areformed of a non-porous, highly etched aluminum foil sheet which may besomewhat less pure (99.7%) respecting aluminum content than the anodelayers. The separator formed of one or more sheet or layer of Kraftpaper saturated and impregnated with a solvent based liquid electrolyteis located between adjacent anode and cathode layers. The anode foilthickness and cathode foil thickness are on the order of 100 micrometersand 20 micrometers, respectively. Most commercial photoflash capacitorscontain a core of separator paper intended to prevent brittle, highlyetched aluminum anode foils from fracturing during winding of the anode,cathode and separator layers into a coiled configuration. Thecylindrical shape and paper core of commercial photoflash capacitorslimits the volumetric packaging efficiency and thickness of an ICD IPGhousing made using same.

[0011] The aluminum anodes and cathodes of aluminum electrolyticcapacitors generally each have at least one tab extending beyond theirperimeters to facilitate electrical connection of all (or sets of) theanode and cathode layers electrically in parallel to form one or morecapacitor and to make electrical connections to the exterior of thecapacitor case. Tab terminal connections for a wound electrolyticcapacitor are described in U.S. Pat. No. 4,663,824 that are laser weldedto feedthrough pin terminals of feedthroughs extending through the case.Wound capacitors usually contain two or more tabs joined together bycrimping or riveting.

[0012] Flat electrolytic capacitors have also been disclosed in theprior art for general applications as well as for use in ICDs. Morerecently developed ICD IPGs employ one or more flat high voltagecapacitor to overcome some of the packaging and volume disadvantagesassociated with cylindrical photoflash capacitors. For example, U.S.Pat. No. 5,131,388 discloses a flat capacitor having a plurality ofstacked capacitor layers. Each capacitor layer contains one or moreanode sheet forming an anode layer having an anode tab, a cathode sheetor layer having a cathode tab and a separator for separating the anodelayer from the cathode layer. In the '388 patent, the electrode stackassembly of stacked capacitor layers is encased within a non-conductive,polymer envelope that is sealed at its seams and fitted into a chamberof a conductive metal, capacitor case or into a compartment of the ICDIPG housing, and electrical connections with the capacitor anode(s) andcathode(s) are made through feedthroughs extending through the case orcompartment wall. The tabs of the anode layers and the cathode layers ofall of the capacitor layers of the stack are electrically connected inparallel to form a single capacitor or grouped to form a plurality ofcapacitors. The aluminum anode layer tabs are gathered together andelectrically connected to a feedthrough pin of an anode feedthroughextending through the case or compartment wall. The aluminum cathodelayer tabs are gathered together and electrically connected to afeedthrough pin of a cathode feedthrough extending through the case orcompartment wall or connected to the electrically conductive capacitorcase wall.

[0013] Many improvements in the design of flat aluminum electrolyticcapacitors for use in ICD IPGs have been disclosed, e.g., thoseimprovements described in “High Energy Density Capacitors forImplantable Defibrillators” presented by P. Lunsmann and D. MacFarlaneat CARTS 96: 16th Capacitor and Resistor Technology Symposium, Mar.11-15 1996, and at CARTS-EUROPE96: 10th European Passive ComponentsSymposium., Oct. 7-11 1996, pp. 35-39. Further features of flatelectrolytic capacitors for use in ICD IPGs are disclosed in U.S. Pat.Nos. 4,942,501; 5,086,374; 5,146,391; 5,153,820; 5,562,801; 5,584,890;5,628,801; and 5,748,439, all issued to MacFarlane et al.

[0014] A number of recent patents including U.S. Pat. No. 5,660,737 andU.S. Pat. Nos. 5,522,851; 5,801,917; 5,808,857; 5,814,082; 5,908,151;5,922,215; 5,926,357; 5,930,109; 5,968,210 and 5,983,472, all assignedto the same assignee, disclose related flat electrolytic capacitordesigns for use in ICDs. In several of these patents, internal alignmentelements are employed as a means for controlling the relative edgespacing of the anode and cathode layers from the conductive capacitorcase. In these patents, each anode layer and cathode layer is providedwith an outwardly extending tab, and the anode and cathode tabs areelectrically connected in common to a feedthrough pin and a step featureof the conductive capacitor case, respectively. The cathode tabs aregathered together against the step feature and ultrasonically weldedtogether and to the step feature. In the '357 patent, the anode tabs arelaser welded to one end of an aluminum ribbon that is ultrasonicallywelded at its other end to an aluminum layer that is ultrasonicallywelded to the terminal pin. The feedthrough terminal pin is electricallyisolated from and extends outside and away from the case to provide ananode connection pin. A cathode connection pin is attached to the caseand extends outwardly therefrom. The anode and cathode connection pinsare electrically connected into the DC-DC converter circuitry, but theattachment mechanism is not described in any detail.

[0015] As noted above, the capacitor layers of a flat electrode stackassembly typically comprise at least one anode layer, a cathode layerand a separator formed of one or more separator sheet. However, it isknown to employ two or more highly etched aluminum foil sheets to forman anode layer of each capacitor layer. The above referenced '890 patentshows three highly etched anode foils or sheets stacked together, andthe above-referenced '082 patent suggests single, double, triple orhigher multiple anode sheets in each capacitor layer. These suggestedcapacitor layers have the same selected number of anode sheets havingthe same anode sheet thickness and therefor would be of uniformthickness for any given capacitor stack Therefore, all of the capacitorlayers or anode-cathode subassemblies of a electrode stack assemblywould be of the same thickness or height.

[0016] It is desirable to achieve the maximum surface area andcapacitance of the electrode stack assembly and minimze empty heightspace of the interior case chamber without causing undue pressure on theelectrode stack assembly as the separator swells upon electrolytefilling.

SUMMARY OF THE INVENTION

[0017] Accordingly, the present invention is directed to providingefficient usage of the space within the interior case chamber of anelectrolytic capacitor particularly adapted for use in IMDs. Thecapacitor is formed with a capacitor or electrode stack assembly havinga stack assembly thickness or height H_(N) that is tailored to fit acase wall height H_(cw) of the capacitor case with minimal wasted spaceand allowance for any stack height tolerance t_(o). The electrode stackassembly comprises a plurality of N stacked capacitor layers each havinga specified capacitor layer thickness or height. The N capacitor layersare preferably formed of a cathode layer, and anode sub-assembly and atleast one separator layer comprising one or more separator sheet oneither side of the cathode layer and the anode sub-assembly.

[0018] At least N₁ capacitor layers have a first capacitor layerthickness T_(CL1) and N₂ capacitor layers have a second capacitor layerthickness T_(CL2) where N=N₁+N₂, and H_(N)=N₁ *T_(CL1)+N₂ *T_(CL2).(plus the thickness of additional upper and lower separatorlayers, if present) The anode sub-assemblies of the N₁ capacitor layerscomprising x anode layers each having anode layer thickness t_(x) thatare stacked together, each anode sub-assembly having an anodesub-assembly thickness T_(x). Similarly, the anode sub-assemblies of theN₂ capacitor layers comprising y anode layers each having anode layerthickness t_(y) that are stacked together, each anode sub-assemblyhaving an anode sub-assembly thickness T_(y).

[0019] In one thickness tailoring embodiment, the x anode layers eachhave the same anode layer thickness t_(x), the y anode layers each havethe same anode layer thickness t_(y), t_(x)=t_(y), and therefore thecondition x≠y is necessary in order to achieve differing anodesub-assembly thicknesses T_(x) and T_(y). In a second tailoringembodiment, the x anode layers each have the same anode layer thicknesst_(x), the y anode layers each have the same anode layer thicknesst_(y), but t_(x)≠t_(y), and therefore either condition x≠y or x=y issufficient in order to achieve differing anode sub-assembly thicknessesT_(x) and T_(y). In a third tailoring embodiment, certain or all of thex anode layers have differing anode layer thicknesses t_(x1), t_(x2), etseq., and certain or all of the y anode layers have differing anodelayer thicknesses t_(y1), t_(y2), et seq., and t_(x1)≠t_(y1),t_(x2)≠t_(y2), et seq., and therefore either condition x≠y or x=y issufficient in order to achieve differing anode sub-assembly thicknessesT_(x) and T_(y). In a fourth tailoring embodiment, certain or all of thex anode layers have differing anode layer thicknesses t_(x1), t_(x2), etseq., and certain or all of the y anode layers have differing anodelayer thicknesses t_(y1), t_(y2) et seq., and t_(x1)=t_(y1),t_(x2)=t_(y2), et seq., and therefore the condition x≠y is necessary inorder to achieve differing anode sub-assembly thicknesses T_(x) andT_(y).

[0020] In a preferred embodiment the electrolytic capacitor is formed ofa capacitor case defining an interior case chamber and case chamberperiphery, an electrode stack assembly of a plurality of stackedcapacitor layers having anode and cathode tabs disposed in the interiorcase chamber, an electrical connector assembly for providing electricalconnection with the anode and cathode tabs through the case, a cover,and electrolyte filling the remaining space within the interior casechamber. A case liner can also be disposed around the electrode stackassembly periphery, and its upper and lower wall thicknesses are takeninto account in specifying the stack height tolerance t_(o).

[0021] The number N of capacitor layers and the overall electrode stackassembly thickness or stack height H_(N) of the N stacked capacitorlayers that are fitted into the interior case chamber depends on thespecified case side wall height H_(cw), and the stack height tolerancet_(o) providing for variances in the stack thickness and any stackbinders or liners holding the stacked capacitor layers together and/orisolating the stack periphery from the case side wall.

[0022] The stack tolerance t_(o) is defined to ensure that the electrodestack assembly, with or without a liner, fits into the interior casechamber after assembly and to allow for separator swelling upon fillingwith electrolyte. The total electrode stack assembly thickness or heightH_(N) is dependent upon the total number N of capacitor layers and thethickness T₁, T₂, . . . T_(n) of the selected groups N₁, N₂, . . . N_(n)of capacitor layers. The capacitor layer thickness T₁, T₂, . . . T_(n)depends on the number and the thickness of the anode foils or sheets ofthe anode layers, the thickness of the cathode layers, and the thicknessof the separator sheets, particularly when swollen by liquidelectrolyte. By this selection, the maximum surface area and capacitanceof the electrode stack assembly is achieved and empty height space ofthe interior case chamber is minimized without causing undue pressure.

[0023] Those of ordinary skill in the art will understand immediatelyupon referring to the drawings, detailed description of the preferredembodiments and claims hereof that many objects, features and advantagesof the capacitors and methods of the present invention will findapplication in the fields other than the field of IMDs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] These and other advantages and features of the present inventionwill be appreciated as the same becomes better understood by referenceto the following detailed description of the preferred embodiment of theinvention when considered m connection with the accompanying drawings,in which like numbered reference numbers designate like parts throughoutthe figures thereof, and wherein:

[0025]FIG. 1 illustrates the physical components of one exemplaryembodiment of an ICD IPG and lead system in which the present inventionmay be advantageously incorporated,

[0026]FIG. 2 is a simplified functional block diagram illustrating theinterconnection of voltage conversion circuitry with the high voltagecapacitors of the present invention with the primary functionalcomponents of one type of an ICD IPG;

[0027] FIGS. 3(a)-3(g) are exploded perspective views of the manner inwhich the various components of the exemplary ICD IPG of FIGS. 1 and 2,including the electrolytic capacitors of the present invention, aredisposed within the housing of the ICD IPG,

[0028]FIG. 4 is an exploded view of one embodiment of a singleanode/cathode layer or electrode stack sub-assembly of an electrolyticcapacitor incorporating the present invention;

[0029]FIG. 5(a) is an exploded perspective view of one embodiment of acold welding apparatus in which anode layers of the electrode stacksub-assembly of FIG. 4 are cold-welded;

[0030]FIG. 5(b) is an unexploded view of the cold welding apparatus ofFIG. 5(a);

[0031]FIG. 5(c) is a cross-sectional view of the cold welding apparatusof FIGS. 5(a) and 5(b) in which anode layers of the electrodesub-assembly of FIG. 4 are cold-welded therein;

[0032]FIG. 6(a) is an exploded top perspective view of one embodiment ofa plurality of capacitor layers of an electrode stack assembly of anelectrolytic capacitor incorporating the present invention;

[0033]FIG. 6(b) is a cross-sectional view of a portion of one embodimentof a cold-welded anode assembly used in the electrolytic capacitor;

[0034]FIG. 6(c) is a cross-sectional view of another portion of oneembodiment of a cold-welded anode assembly used in the electrolyticcapacitor;

[0035]FIG. 7 is a top perspective view of one embodiment of an electrodestack assembly of an electrolytic capacitor incorporating the presentinvention;

[0036]FIG. 8 is an enlarged view of a portion of the electrode stackassembly shown in FIG. 7;

[0037]FIG. 9 is an exploded top perspective view of one embodiment of acapacitor of the present invention employing the electrode stackassembly of FIGS. 6, 7 and 8 therein;

[0038]FIG. 10(a) is an exploded top perspective view of the partiallyassembled capacitor of FIG. 9;

[0039]FIG. 10(b) is a partial cross-section view of the case base andside wall of FIG. 10(a);

[0040]FIG. 11 is a top view of one embodiment of a partly assembledcapacitor of the present invention having no cover disposed thereon;

[0041]FIG. 12 is a top perspective view of the capacitor of FIG. 11having a cover disposed thereon.

[0042]FIG. 13 is a partial cross-section view of the case periphery andelectrode stack periphery taken along lines 13-13 of FIG. 11 depictingperipheral edges of anode subassemblies, cathode layers, and separatorlayers of a portion of the stack height of the electrode stack assembly,

[0043]FIG. 14 is a perspective view of one embodiment of a fullyassembled capacitor of the present invention having a case liner and nocover disposed thereon; and

[0044]FIG. 15 is a perspective view of the case liner of FIG. 14 placedaround the periphery of the electrode stack assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045]FIG. 1 illustrates one embodiment of ICD IPG 10 in which thecapacitor of the present invention is advantageously incorporated, theassociated ICD electrical leads 14, 16 and 18, and their relationship toa human heart 12. The leads are coupled to ICD IPG 10 by means ofmulti-port connector block 20, which contains separate connector portsfor each of the three leads illustrated. Lead 14 is coupled tosubcutaneous electrode 30, which is intended to be mountedsubcutaneously in the region of the left chest. Lead 16 is a coronarysinus lead employing an elongated coil electrode which is located in thecoronary sinus and great vein region of the heart. The location of theelectrode is illustrated in broken line format at 32, and extends aroundthe heart from a point within the opening of the coronary sinus to apoint in the vicinity of the left atrial appendage.

[0046] Lead 18 is provided with elongated electrode coil 28 which islocated in the right ventricle of the heart. Lead 18 also includesstimulation electrode 34 which takes the form of a helical coil which isscrewed into the myocardial tissue of the right ventricle. Lead 18 mayalso include one or more additional electrodes for near and far fieldelectrogram sensing.

[0047] In the system illustrated, cardiac pacing pulses are deliveredbetween helical electrode 34 and elongated electrode 28. Electrodes 28and 34 are also employed to sense electrical signals indicative ofventricular contractions. As illustrated, it is anticipated that theright ventricular electrode 28 will serve as the common electrode duringsequential and simultaneous pulse multiple electrode defibrillationregimens. For example, during a simultaneous pulse defibrillationregimen, pulses would simultaneously be delivered between electrode 28and electrode 30 and between electrode 28 and electrode 32. Duringsequential pulse defibrillation, it is envisioned that pulses would bedelivered sequentially between subcutaneous electrode 30 and electrode28 and between coronary sinus electrode 32 and right ventricularelectrode 28. Single pulse, two electrode defibrillation shock regimensmay be also provided, typically between electrode 28 and coronary sinuselectrode 32. Alternatively, single pulses may be delivered betweenelectrodes 28 and 30. The particular interconnection of the electrodesto an ICD will depend somewhat on which specific single electrode pairdefibrillation shock regimen is believed more likely to be employed.

[0048]FIG. 2 is a block diagram illustrating the interconnection of highvoltage output circuit 40, high voltage charging circuit 64 andcapacitors 265 according to one example of the microcomputer basedoperating system of the ICD IPG of FIG. 1. As illustrated, the ICDoperations are controlled by means of a stored program in microprocessor42, which performs all necessary computational functions within the ICD.Microprocessor 42 is linked to control circuitry 44 by means ofbi-directional data/control bus 46, and thereby controls operation ofthe output circuitry 40 and the high voltage charging circuitry 64.Pace/sense circuitry 78 awakens microprocessor 42 to perform anynecessary mathematical calculations, to perform tachycardia andfibrillation detection procedures and to update the time intervalscontrolled by the timers in pace/sense circuitry 78 on reprogramming ofthe ICD operating modes or parameter values or on the occurrence ofsignals indicative of delivery of cardiac pacing pulses or of theoccurrence of cardiac contractions,.

[0049] The basic operation and particular structure or components of theexemplary ICD of FIGS. 1 and 2 may correspond to any of the systemsknown in the art, and the present invention is not dependent upon anyparticular configuration thereof The flat aluminum electrolyticcapacitor of the present invention may be employed generally inconjunction with the various systems illustrated in the aforementioned'209 patent, or in conjunction with the various systems or componentsdisclosed in the various U.S. patents listed in the above-referencedparent patent application Ser. No. 09/103,843.

[0050] Control circuitry 44 provides three signals of primary importanceto output circuitry 40. Those signals include the first and secondcontrol signals discussed above, labeled here as ENAB, line 48, andENBA, line 50. Also of importance is DUMP line 52 which initiatesdischarge of the output capacitors and VCAP line 54 which provides asignal indicative of the voltage stored on the output capacitors C1, C2,to control circuitry 44. Defibrillation electrodes 28, 30 and 32illustrated in FIG. 1, above, are shown coupled to output circuitry 40by means of conductors 22, 24 and 26. For ease of understanding, thoseconductors are also labeled as “COMMON”, “HVA” and “HVB”. However, otherconfigurations are also possible. For example, subcutaneous electrode 30may be coupled to HVB conductor 26, to allow for a single pulse regimento be delivered between electrodes 28 and 30. During a logic signal onENAB, line 48, a cardioversion/defibrillation shock is delivered betweenelectrode 30 and electrode 28. During a logic signal on ENBA, line 50, acardioversion/defibrillation shock is delivered between electrode 32 andelectrode 28.

[0051] The output circuitry includes a capacitor bank, includingcapacitors C1 and C2 and diodes 121 and 123, used for deliveringdefibrillation shocks to the electrodes. Alternatively, the capacitorbank may include a further set of capacitors as depicted in the abovereferenced '758 application. In FIG. 2, capacitors 265 are illustratedin conjunction with high voltage charging circuitry 64, controlled bythe control/timing circuitry 44 by means of CHDR line 66. Asillustrated, capacitors 265 are charged by means of a high frequency,high voltage transformer 65. Proper charging polarities are maintainedby means of the diodes 121 and 123. VCAP line 54 provides a signalindicative of the voltage on the capacitor bank, and allows for controlof the high voltage charging circuitry and for termination of thecharging function when the measured voltage equals the programmedcharging level.

[0052] Pace/sense circuitry 78 includes an R-wave sense amplifier and apulse generator for generating cardiac pacing pulses, which may alsocorrespond to any known cardiac pacemaker output circuitry and includestiming circuitry for defining ventricular pacing intervals, refractoryintervals and blanking intervals, under control of microprocessor 42 viacontrol/data bus 80.

[0053] Control signals triggering generation of cardiac pacing pulses bypace/sense circuitry 78 and signals indicative of the occurrence ofR-waves, from pace/sense circuitry 78 are communicated to controlcircuitry 44 by means of a bi-directional data bus 81. Pace/sensecircuitry 78 is coupled to helical electrode 34 illustrated in FIG. 1 bymeans of a conductor 36. Pace/sense circuitry 78 is also coupled toventricular electrode 28, illustrated in FIG. 1, by means of a conductor82, allowing for bipolar sensing of R-waves between electrodes 34 and 28and for delivery of bipolar pacing pulses between electrodes 34 and 28,as discussed above.

[0054] FIGS. 3(a) through 3(g) show perspective views of variouscomponents of ICD IPG 10, including one embodiment of the capacitor ofthe present invention, as those components are placed successivelywithin the housing of ICD IPG 10. In FIG. 3(a), electronics module 360is placed in right-hand shield 340 of ICD IPG 10. FIG. 3(b) shows ICDIPG 10 once electronics module 360 has been seated in right-hand shield340.

[0055]FIG. 3(c) shows a pair of capacitors 265 formed as describedherein prior to being placed within right-hand shield 340, thecapacitors 265 being connected electrically in series byinterconnections in electronics module 340. FIG. 3(d) shows ICD IPG 10once the pair of capacitors 265 has been placed within right-hand shield340.

[0056]FIG. 3(e) shows insulator cup 370 prior to its placing atopcapacitors 265 in right-hand shield 340. FIG. 3(f) shows electrochemicalcell or battery 380 having insulator 382 disposed around battery 380prior to placing it in shield 340. Battery 380 provides the electricalenergy required to charge and re-charge capacitors 265, and also powerselectronics module 360. Battery 380 may take any of the forms employedin the prior art to provide cardioversion/defibrillation energy, some ofwhich are identified in parent patent application Ser. No. 09/103,843;.

[0057]FIG. 3(g) shows ICD IPG 10 having left-hand shield 350 connectedto right-hand shield 340 and feedthrough 390 projecting upwardly fromboth shield halves. Activity sensor 400 and patient alert apparatus 410are shown disposed on the side lower portion of left-hand shield 350.Left-hand shield 350 and right-hand shield 340 are subsequently closedand sealed (not shown in the figures).

[0058] The present invention is directed to the tailoring of thethickness or height of an electrode stack assembly comprising one ormore capacitor layers to the thickness or height of a capacitor casethat the electrode stack assembly is fitted into. The preferredembodiment of the present invention is illustrated and described belowin the context of a capacitor enclosure formed of two parts, a case anda cover, wherein the case defines an interior case chamber that isclosed by the cover. The preferred case has a base having a baseperipheral edge and a case side wall extending between the baseperipheral edge to a side wall opening edge defining a case openingedge. The base is larger dimensionally than the side walls, and thecover is shaped to about the same dimensions as the base. The cover issealed against the case opening edge to enclose the interior casechamber which has a case chamber periphery and a case height H_(cw) asshown in FIG. 10(b) and described further below. Thus, in this caseconfiguration, the cover and base are the opposed major surfaces of theenclosure and are separated by the case side wall. The electrode stackassembly has a stack height that is correlated to the case height H_(cw)as shown in FIG. 10(b) and described further below.

[0059] However, it will be understood that the case and cover may take avariety of differing forms, and that the principles of the presentinvention may be applied to any such form. For example, two opposed caseside walls may be dimensionally larger than the case base and the coverin the manner of a canister wherein the enclosure can be characterizedby a case width between the opposed side walls. In this case and theelectrode stack assembly is inserted through the end opening and betweenthe opposed major case side walls. The electrode stack height of such anelectrode stack assembly is tailored to the case width in accordancewith the teachings of the present invention. Consequently, the term“case height” embraces a case side wall height or a case width or a casethickness that the electrode stack assembly fits into in the stackheight dimension.

[0060]FIG. 4 shows an exploded view of one embodiment of a capacitorlayer or single anode/cathode sub-assembly 227 of capacitor 265. Thecapacitor design described herein employs a stacked configuration of aplurality of capacitor layers or single anode/cathode sub-assemblies 227as further described below with respect to FIG. 6. Each anode/cathodesub-assembly 227 comprises alternating substantially rectangular-shapedanode layers 185 and cathode layers 175, with a substantiallyrectangular-shaped separator layer 180 being interposed therebetween.The shapes of anode layers 185, cathode layers 175 and separator layers180 are primarily a matter of design choice, and are dictated largely bythe shape or configuration of case 90 within which those layers areultimately disposed. Anode layers 185, cathode layers 175 and separatorlayers 180 may assume any arbitrary shape to optimize packagingefficiency.

[0061] Anode sub-assembly 170 d most preferably comprises a plurality ofnon-notched anode layers 185 a, 185 b, 185 c, notched anode layer 190including anode tab notch 200, and anode tab 195 coupled to anode layer185 a. It will be understood that anode sub-assembly 170 d shown in FIG.4 is but one possible embodiment of an anode sub-assembly 170. Cathodelayer 175 d most preferably is formed of a single sheet and has cathodetab 176 formed integral thereto and projecting from the peripherythereof

[0062] In one preferred embodiment of the sub-assembly 227 as depictedin the figures, two individual separator layer sheets 180 a and 180 bform the separator layer 180 that is disposed between each anodesub-assembly 170 and cathode layer 175. Further single separator layersheets 180 a and 180 b are disposed against the outer surfaces of theanode layer 185 c and the cathode layer 175 d. When the sub-assembliesare stacked, the outermost single separator layer sheets 180 a and 180 bbear against adjacent outermost single separator layer sheets 180 b and180 a, respectively, of adjacent capacitor layers so that two sheetseparator layers 180 separate all adjacent cathode and anode layers ofan electrode stack assembly 225.

[0063] It will be understood by those skilled in the art that theprecise number of subassemblies 227 selected for use in a electrodestack assembly 225 will depend upon the energy density, volume, voltage,current, energy output and other requirements placed upon capacitor 265.Similarly, it will be understood by those skilled in the art that theprecise number of notched and un-notched anode layers 185, anode tabs195, anode sub-assemblies 170, cathode layers 175 and separator layers180 selected for use in a given embodiment of anode/cathode sub-assembly227 will depend upon the energy density, volume, voltage, current,energy output and other requirements placed upon capacitor 265.

[0064] In accordance with the present invention as described below inreference to FIG. 13, the number of anode layers 185 a, 185 b, 185 c andnotched anode layer 190 of any given anode sub-assembly 170 is tailoredto provide a specific desired thickness of the capacitor layer orsub-assembly 227. The capacitor layer thickness T₁, T₂, . . . T_(n)depends on the number and the thickness of the anode foils or sheets ofthe anode layers, the thickness of the cathode layers, and the thicknessof the separator sheets, particularly when swollen by liquidelectrolyte. The total electrode stack assembly thickness or heightH_(N) is dependent upon the total number N of capacitor layers and thethickness T₁, T₂, . . . T_(n) of selected groups N₁, N₂, . . . N_(n) ofcapacitor layers. The anode sub-assemblies 170 of a first group of N₁capacitor layers each comprise x anode layers 185, 190 each having ananode layer thickness t_(x) that are welded together as described belowin reference to FIGS. 5 and 6, whereby each anode sub-assembly 170therefore has an anode sub-assembly thickness T_(x). The anodesub-assemblies 170 of a second group of N₂ capacitor layers eachcomprise y anode layers 185, 190 each having an anode layer thicknesst_(y) that are welded together in the same manner, whereby each anodesub-assembly has an anode sub-assembly thickness T_(y). Further groupsof capacitor layers 170 can be devised in this manner.

[0065] It will now become apparent that a virtually unlimited number ofcombinations and permutations respecting the number of anode/cathodesub-assemblies 227, and the number of un-notched and notched anodelayers 185 forming anode sub-assembly 170, anode sub-assemblies 170,anode tabs 195, cathode layers 175 and separator layers 180 disposedwithin each anode/cathode sub-assembly 227, may be selected according tothe particular requirements of capacitor 265. Anode layers 185, cathodelayers 175 and separator layers 180 are most preferably formed ofmaterials typically used in high quality aluminum electrolyticcapacitors.

[0066] Anode layers 185 and 190 are formed of anode foil that is mostpreferably through-etched, has a high specific capacitance (at leastabout 0.3, at least about 0.5 or most preferably at least about 0.8microfarads/cm²), has a dielectric withstand parameter of at least 425Volts DC, a thickness ranging between about 50 and about 200micrometers, more preferably between about 75 and 150 micrometers, morepreferably yet between about 90 and about 125 micrometers, and mostpreferably being about 100 micrometers thick, and a cleanliness of about1.0 mg/m² respecting projected area maximum chloride contamination. Theanode foil preferably has a rated surge voltage of 390 Volts, an initialpurity of about 99.99% aluminum, a final thickness of about 104micrometers, plus or minus about five micrometers, and a specificcapacitance of about 0.8 microfarads per square centimeter. Suitableanode foils are commercially available on a widespread basis.

[0067] Individual anode layers 185 are typically somewhat stiff andformed of high-purity aluminum processed by etching to achieve highcapacitance per unit area. Thin anode foils are preferred, especially ifthey substantially maintain or increase specific capacitance whilereducing the thickness of the electrode stack assembly 225, or maintainthe thickness of electrode stack assembly 225 while increasing overallcapacitance. For example, it is contemplated that individual anodelayers 185 have a thickness of about 10 micrometers, about 20micrometers, about 30 micrometers, about 40 micrometers, about 50micrometers, about 60 micrometers, about 70 micrometers, about 80micrometers, about 90 micrometers, about 100 micrometers, about 110micrometers, about 120 micrometers, about 130 micrometers, about 140micrometers and about 150 micrometers.

[0068] Cathode layers 175 are preferably high purity and arecomparatively flexible. Cathode layers 175 are most preferably formedfrom cathode foil having high surface area (i.e., highly etched cathodefoil), high specific capacitance (preferably at least 200microfarads/cm², and at least 250 microfarads/cm² when fresh), athickness of about 30 micrometers, a cleanliness of about 1.0 mg/m²respecting projected area maximum chloride contamination, and a puritywhich may be less than corresponding to the staring foil material fromwhich anode foil is made. The cathode foil preferably has an initialpurity of at least 99% aluminum, and more preferably yet of about 99.4%aluminum, a final thickness of about 30 micrometers, and an initialspecific capacitance of about 250 microfarads per square centimeter. Inother embodiments, cathode foil has a specific capacitance rangingbetween about 100 and about 500 microfarads/cm², about 200 and about 400microfarads/cm², or about 250 and about 350 microfarads/cm², a thicknessranging between about 10 and about 150 micrometers, about 15 and about100 micrometers, about 20 and about 50 micrometers, or about 25 andabout 40 micrometers.

[0069] It is generally preferred that the specific capacitance of thecathode foil be as high as possible, and that cathode layer 175 be asthin as possible. For example, it is contemplated that individualcathode layers 175 have specific capacitances of about 100microfarads/cm², about 200 microfarads/cm², about 300 microfarads/cm²,about 400 microfarads/cm², about 500 microfarads/cm², about 600microfarads/cm², about 700 microfarads/cm², about 800 microfarads/cm²,about 900 microfarads/cm², or about 1,000 microfarads/cm². Suitablecathode foils are commercially available on a widespread basis. In stillother embodiments, cathode foil is formed of materials or metals inaddition to aluminum, aluminum alloys and “pure” aluminum.

[0070] Separator layer sheets 180 a and 180 b outer separator layers 165a and 165 b are most preferably made from a roll or sheet of separatormaterial. Separator layers 180 are preferably cut slightly larger thananode sub-assemblies 170 and cathode layers 175 to accommodatemisalignment during the stacking of layers, to prevent subsequentshorting between anode and cathode layers, and to otherwise ensure thata physical barrier is disposed between the anodes and the cathodes ofthe finished capacitor. In accordance with the present invention, theanode sub-assemblies 170 are also cut larger than the cathode layers175.

[0071] It is preferred that separator layer sheets 180 a and 180 b andexterior separator layers 165 a and 165 b (shown in FIG. 9) be formed ofa material that: (a) is chemically inert; (b) is chemically compatiblewith the selected electrolyte; (c) may be impregnated with theelectrolyte to produce a low resistance path between adjoining anode andcathode layers, and (d) physically separates adjoining anode and cathodelayers. In one preferred embodiment, separator material is a purecellulose, very low halide or chloride content Kraft paper having athickness of about 0.0005 inches (0.0013 mm), a density of about 1.06grams/cm³, a dielectric strength of 1,400 Volts AC per 0.001 inch (0.025mm) thickness, and a low number of conducting paths (about 0.4/ft² orless). Separator layer sheets 180 a and 180 b and outer separator layers165 a and 165 b may also be formed of materials other than Kraft paper,such as Manila paper, porous polymeric materials or fabric gauzematerials. For example, porous polymeric materials may be disposedbetween anode and cathode layers like those disclosed in U.S. Pat. No.3,555,369 and 3,883,784 in some embodiments of the capacitor layers

[0072] In such capacitor stacks formed of a plurality of capacitorlayers, a liquid electrolyte saturates or wets separator layers 180 andis disposed within case 90. It is to be understood, however, thatvarious embodiments include within their scope a solid or adhesiveelectrolyte such as those disclosed in U.S. Pat. Nos., 5,628,801;5,584,890; 4,942,501; 5,146,391 and 5,153,820. Note that an appropriateinter-electrode adhesives/electrolyte layer may be employed in place ofpaper, gauze or porous polymeric materials to form separator layer 180.

[0073] Continuing to refer to FIG. 4, a first preferred step inassembling a flat aluminum electrolytic capacitor is to cut anode layers185 and 190, anode tabs 195, cathode layers 175 and separator layers180. Those components are most preferably cut to shape using dies havinglow wall-to-wall clearance, where inter-wall spacing between thesubstantially vertically-oriented corresponding walls of the punch anddie is most preferably on the order of about 6 millionths of an inch perside. Larger or smaller inter-wall spacings between the substantiallyvertically-oriented corresponding walls of the punch and cavity, such asabout 2, about 4, about 5, about 7, about 8, about 10 and about 12millionths of an inch may also be employed but are less preferred.

[0074] Such low clearance results in smooth, burr free edges beingformed along the peripheries of anode layers 185 and 190, anode tabs195, cathode layers 175 and separator layers 180. Smooth, burr freeedges on the walls of the dies have been discovered to be criticalrespecting reliable performance of a capacitor. The presence of burrsalong the peripheries of anode layers 185 and 190, anode tabs 195,cathode layers 175 and separator layers 180 may result in short circuitand failure of the capacitor. The means by which anode foil, cathodefoil and separator materials are cut or formed may have a significantimpact on the lack or presence of burrs and other cutting debrisdisposed about the peripheries of the formed or cut members. The use oflow clearance dies produces an edge superior to the edge produced byother cutting methods, such as steel rule dies. The shape, flexibilityand speed of a low clearance die have been discovered to be superior tothose achieved by laser or blade cutting. Other methods of cutting orforming anode layers 185 and 190, anode tabs 195, cathode layers 175 andseparator layers 180 include, but are not limited to, steel rule diecutting, laser cutting, water jet cutting and blade cutting.

[0075] The preferred low clearance of the die apparatus is especiallyimportant for cutting thin ductile materials such as the cathode foil.In addition to improving reliability, burr and debris reduction permitsreductions in the thickness of separator layer 180, thereby improvingenergy density of the capacitor. Angle cutting, where the face of thepunch is not held parallel to the opposing floor of the die during thecutting step, is another less preferred method of cutting or forminganode layers 185 and 190, anode tabs 195, cathode layers 175 andseparator layers 180.

[0076] In a preferred method, foil or separator materials are drawnbetween the punch and cavity portions of a die having appropriateclearances on a roll. An air or hydraulically actuated press is thenmost preferably employed to actuate the punch or cavity portion of thedie. The punch portion of the die is most preferably formed of hardenedtool steel, or has other suitable wear resistant materials or coatingsdisposed on the cutting surfaces thereof When the cavity of the die isaligned vertically, the punch portion of the die may travel eitherupwards or downwards towards the die cavity during a cutting cycle. Inthe former case, components are cut and drop downwardly into a containerfor use in subsequent assembly operations. In the latter case,components are cut and may be presented directly to automated assemblyequipment, such as robots equipped with vacuum or other pick-up tooling,for subsequent processing. Low clearance dies of the type describedherein may be supplied by Top Tool, Inc. of Minneapolis, Minn.,

[0077] Anode sub-assembly 170 most preferably includes one notched anodelayer 190, which facilitates appropriate placing and positioning ofanode tab 195 within anode sub-assembly 170. More than one notched anodelayer 190 may also be included in anode sub-assembly 170. It ispreferred that the remaining anode layers of anode sub-assembly 170 benon-notched anode layers 185. Anode tab 195 is most preferably formed ofaluminum strip material. In one preferred embodiment, the aluminum stripmaterial has a purity of about 99.99% aluminum and a lesser degree ofanodization than the anode foil. When anode tab 195 is formed of anon-anodized material, cold welding of anode tab 195 to non-notchedanode layers 185 may be accomplished with less force and deflection,more about which we say below. It is preferred that the thickness ofanode tab 195 be about equal to that of notched anode layer 190. If morethan one notched anode layer 190 is employed in anode sub-assembly 170,a thicker anode tab 195 may be employed.

[0078] Referring now to FIGS. 5(a) through 5(c), two non-notched anodelayers 185 a and 185 b are placed on cold welding fixture base layer 207of cold welding apparatus 202. The various structural members of coldwelding apparatus 202 are most preferably formed of precision machinedstainless steel or a high strength aluminum alloy. Layers 185 a and 185b are next aligned and positioned appropriately on cold welding fixturebase layer 207 using spring loaded alignment pins 209 a through 209 e.Pins 209 a through 209 e retract upon top layer 208 being presseddownwardly upon layers 185 a and 185 b disposed within cold weldingcavity 220. See also FIG. 5(c), where a cross-sectional view of coldwelding apparatus 202 is shown.

[0079] Anode layer 190 is similarly disposed within cavity 220, followedby placing anode tab 195 within anode tab notch 200 in notched anodelayer 190. Anode tab 195 is most preferably positioned along theperiphery of notched anode layer 190 with the aid of additional springloaded alignment pins 209 f and 209 g disposed along the periphery ofanode tab 195. Non-notched anode layer 185 c is then placed atop anodelayer 190. Stacked anode sub-assembly 170 is then clamped between topplate 208 and base plate 207. Disposed within base plate 207 are anodelayer cold welding pins 206 a and anode tab cold welding pin 211 a.Disposed within top plate 208 are anode layer cold welding pin 206 b andanode tab cold welding pin 211 b. Base plate 207 and top plate 208 arealigned such that the axes of cold welding pins 206 a and 206 b coincidewith and are aligned respecting corresponding cold welding pins 211 aand 211 b.

[0080] Upper actuation apparatus 214 of cold welding apparatus 202displaces cold welding pins 206 b and 211 b downwardly. Lower actuationapparatus 215 displaces cold welding pins 206 a and 211 a upwardly. Inone embodiment of upper actuation apparatus 214 and lower actuationapparatus 215, pneumatic cylinders are employed to move pins 206 a, 206b, 211 a and 211 b. In another embodiment of apparatus 214 and apparatus215, a pair of rolling wheels is provided that move simultaneously andperpendicularly to the axes of pins 206 a, 206 b, 211 a, and 211 b.Still other embodiments of apparatus 214 and apparatus 215 may employhydraulic actuators, cantilever beams, dead weights, springs,servomotors electromechanical solenoids, and the like for moving pins206 a, 206 b, 211 a and 211 b. Control of actuation apparatus 214 andapparatus 215 respecting pin displacement force magnitude and timing maybe accomplished using any one or combination of constant load, constantdisplacement, solenoid controller, direct or indirect means.

[0081] Following clamping with top plate 208, cold welding pins 206 a,206 b, 211 a and 211 b are actuated. Cold welds 205 and 210 in anodesub-assembly 170 are formed by compression forces generated when coldweld pins 206 a, 206 b, 211 a and 211 b are compressed against anodesub-assembly 170. See FIG. 6(a), where the preferred regions in whichcold welds 205 and 210 are formed are shown. Cold welds 205 and 210 maybe described as not only cold welds, but forged welds. This is becausethe interfacial boundaries between anode layers 185 are deformed in theregion of welds 205 and 210, thereby disrupting oxide layers andbringing base metals into direct contact with one another where metallicbonding occurs. Metallic bonding increases the strength of the welds.

[0082] In one embodiment of the method, a plurality of pneumaticcylinders function simultaneously in upper actuation apparatus 214 andlower actuation apparatus 215 to drive pins 206 a, 206 b, 211 a and 211b against anode sub-assembly 170. Anode layer cold weld 205 and anodetab cold weld 210 are most preferably formed under direct constant loadconditions, where pneumatic cylinders are pressurized to a predeterminedfixed pressure. Anode layer cold weld 205 and anode tab cold weld 210may also be formed under indirect constant displacement conditions,where pneumatic cylinders are pressurized until a displacement sensorplaced across cold welding pins 206 a, 206 b, 211 a or 211 b generates asignal having a predetermined value, whereupon those pins are disengagedfrom anode/cathode sub-assembly 227.

[0083] In another embodiment of the method, a cantilever beam mechanismis incorporated into upper actuation apparatus 214 and lower actuationapparatus 215. Anode layer cold weld 205 and anode tab cold weld 210 areformed under direct constant displacement conditions, where cantileverbeams are actuated and cause upper and lower members 208 and 207 toengage anode/cathode sub-assembly 227 until a hard stop point isreached. An indirect load controlled system may also be employed inapparatus 214 and apparatus 215, where cantilever or other means includea load measuring sensor for controlling the stop point of the cantileverbeam, for example, when a predetermined load is measured by the sensor.

[0084] The cross-sectional shape of cold weld pins 206 a, 206 b, 211 aand 211 b may be square, circular, oval or any other suitable shape. Theshape of the ends of cold weld pins 206 a, 206 b, 211 a and 211 b may beflat, rounded, domed or any other suitable shape appropriate forselectively controlling the properties of the cold welds producedtherein. Likewise, more or fewer than four cold weld pins may beemployed. The ends of cold weld pins 206 a, 206 b, 211 a and 211 b aremost preferably rounded or domed and circular in cross-section. Coldweld pins 206 a, 206 b, 211 a and 211 b preferably have a diameter ofabout 0.060 inches (0.174 mm) and further have a beveled or radiusedend. Cold weld pins 206 a, 206 b, 211 a and 211 b are preferably madefrom a high strength material that does not readily deform under thepressures obtained during welding, such as stainless steel, titanium,tool steel or HSLA steel. The ends or side walls of cold welding pins206 a, 206 b, 211 a and 211 b may be coated, clad or otherwise modifiedto increase wear resistance, deformation resistance or other desirabletribilogical attributes of the pins.

[0085] The primary function of cold welds 205 and 210 is to provideelectrical interconnections between layers 185 a, 185 b, 185 c and 190and anode tab 195, while minimizing the overall thickness of anodesub-assembly 170 in the regions of welds 205 and 210. Typical prior artcommercial cylindrical capacitors exhibit a significant increase in thethickness of the anode layer in the regions of the cold welds. Thisincrease in thickness is typically on the order of about two times thethickness of the tab, or about 0.008 inch (0.020 mm). In the case ofcylindrical capacitors where only one or two non-coincident tabconnections are present, the overall effect on anode layer thickness maybe minimal. In a stacked layer design having many more interconnectionsand welds, however, increases in weld zone thickness have been found tosignificantly increase the overall thickness of the anode layer and theelectrode stack assembly as a whole.

[0086] In one cold welding method and corresponding apparatus, no or aninappreciable net increase in anode sub-assembly 170 thickness resultswhen cold weld geometries and formation processes are appropriatelyoptimized. Several embodiments of anode-assembly 170 have been found tohave no more than about a 20% increase in layer thickness due to thepresence of cold welds, as compared to about a 200% increase inthickness resulting from cold welds found in some commercial cylindricalcapacitors. Two, three, four, five, six or more anode layers 185 and 190may be cold-welded to form anode sub-assembly 170 as described herein.

[0087]FIG. 6(b) shows a cross-sectional view of a portion of oneembodiment of a cold-welded anode assembly formed in accordance with thepreferred cold welding method. Anode layers 185 a, 190, 185 b and 185 chaving anode layer thicknesses t_(a), t_(N), t_(b) and t_(c),respectively, are cold-welded together at weld 205 through thecompressive action of pins 206 a and 206 b mounted in bottom plate 207and top plate 208, respectively. Pins 206 a and 206 b form centraldepressions 293 and 294, respectively, in anode sub-assembly 170 d, andfurther result in the formation of rims 295 and 296, respectively. Rims295 and 296 project downwardly and upwardly, respectively, from thesurrounding surfaces of anode sub-assembly 170 d, thereby increasing theoverall thickness T of anode sub-assembly 170 d by ΔT (T measured inrespect of the non-cold-welded surrounding regions or portions of anodesub-assembly 170 d).

[0088]FIG. 6(c) shows a cross-sectional view of another portion of oneembodiment of a cold-welded anode assembly wherein anode layers 185 a,185 b and 185 c and anode tab 195, having anode layer/tab thicknessest_(a), t_(b), t_(c) and t_(tab), respectively, are cold-welded togetherat weld 210 through the compressive action of pins 211 a and 211 bmounted in bottom plate 207 and top plate 208, respectively. Pins 211 aand 211 b form central depressions 297 and 298, respectively, in anodesub-assembly 170 d, and further result in the formation of rims 299 and301, respectively. Rims 299 and 301 project downwardly and upwardly,respectively, from the surface of anode sub-assembly 170 d, therebyincreasing overall thickness T of anode sub-assembly 170 d by ΔT (Tmeasured in respect of the non-cold-welded surrounding regions orportions of anode sub-assembly 170 d).

[0089] The overall thickness T of anode sub-assembly 170 d is thereforedefined by the equation:

T=nt

[0090] The maximum overall thickness T+ΔT of anode sub-assembly 170 d inthe region of cold welds 205 or 210 is then defined by the equation:

T+ΔT=nt+ΔT

[0091] where T_(as) is the overall thickness of anode sub-assembly 170 din non-cold-welded regions, n is the number of anode layers 185 and/or190 in anode sub-assembly 170 d, and t is the thickness of individualanode layers 185 and/or 190 or anode tab 195 where the thicknessest_(n), t_(a), t_(b), t_(c) and t_(tab), are assumed to be the same.

[0092] It is highly desirable to form anode sub-assembly such that theratio ΔT/T is less than or equal to 0.05, 0.1, 0.15, 0.20, 0.25, 0.30,0.35, 0.40, 0.45 or 0.50. The lower the value of the ratio ΔT/T, thegreater the volumetric efficiency of capacitor 265. Additionally, theoverall thickness of capacitor 265 may be reduced when the value of theratio ΔT/T is made smaller.

[0093] Referring now to FIG. 6(a), the overall thickness of electrodestack assembly 225 may be reduced farther by staggering or offsettinghorizontally the respective vertical locations of tabs 195 a through 195h (and corresponding cold welds 210). In this embodiment, tabs 195 a 195b, for example, are not aligned vertically in respect of one another.Such staggering or offsetting of tabs 195 permits the increases inthickness ΔT corresponding to each of anode subassemblies 170 a through170 h to be spread out horizontally over the perimeter or other portionof electrode stack assembly 225 such that increases in thickness ΔT donot accumulate or add constructively, thereby decreasing the overallthickness of electrode stack assembly 225. Cold welds 205 may similarlybe staggered or offset horizontally respecting one another and cold weld210 to achieve a reduction in overall thickness of electrode stackassembly 225.

[0094] In another preferred embodiment, the anode sub-assembly 170 ofeach capacitor layer or electrode sub-assembly comprises a plurality ofthree, four, five or more anode sheets or layers 185 and 190, eachsub-assembly most preferably having at least one anode layer having acorresponding anode tab 195 attached thereto or forming a portionthereof, the layers being cold welded together to form anodesub-assembly 170. For example, an anode sub-assembly 170 may comprisesix anode layers 185 constructed by cold-welding two separate tripleanode layers 185 that were previously and separately cold-welded orotherwise joined together. Alternatively, anode sub-assembly 170 layermay comprise seven anode layers constructed by cold-welding together onetriple anode layer 185 and one quadruple anode layer 185 that werepreviously and separately cold-welded or otherwise joined together. Inanother preferred embodiment, multiple notched anode layers 190 mayemployed in anode sub-assembly 170, thereby permitting the use of athicker anode tab material.

[0095] The geometry of base plate 207 and top plate 208 in the regionssurrounding cold welding pins 206 a, 206 b, 211 a and 211 b has beendiscovered to affect the properties of cold welds 205 and 210. In apreferred method, the mating surfaces of plates 207 and 208 surfaceshave no radiused break formed in the perimeters of the pin holes. Thepresence of radiused breaks or chamfers in those regions may causeundesired deformation of cold welds 205 and 210 therein. Suchdeformation may result in an increase in the thickness of anodesub-assembly 170, which may translate directly into an increase in thethickness of capacitor 265. Note further that the increase in thicknessso resulting is a multiple of the number of anode sub-assemblies 170present in electrode stack assembly 225. Alternatively, radiused breaksor chamfers may be employed in the region of the pin holes in base plate207 and top plate 208, but appropriate capacitor design accommodationsare most preferably made, such as staggering the positions of adjoiningstacked cold welds.

[0096] Once cold welding pins 206 a, 206 b, 211 a and 211 b have beenactuated against anode sub-assembly 170, top plate 208 is removed andcold-welded anode sub-assembly 170 is provided for further stacking ofanode/cathode sub-assembly 227. As illustrated in FIGS. 4, and 6(a),this illustrated embodiment of electrode stack assembly 225 mostpreferably comprises a plurality of cold-welded anode sub-assemblies 175a through 175 h, a plurality of cathode layers 175 a through 175 i aplurality of separator layers 180 a and 180 b, outer separator layers165 a and 165 b, outer wrap 115 and wrapping tape 245.

[0097] Outer wrap 115 is most preferably die cut from separator materialdescribed supra, but may be formed from a wide range of other suitablematerials such as polymeric materials, aluminum, suitable heat shrinkmaterials, suitable rubberized materials and synthetic equivalents orderivatives thereof and the like. Wrapping tape 245 is most preferablycut from a polypropylene-backed acrylic adhesive tape, but may also bereplaced by a staple, an ultrasonic paper joint or weld, suitableadhesives other than acrylic adhesive, suitable tape other thanpolypropylene-backed tape, a hook and corresponding clasp and so on.

[0098] Outer wrap 115 and wrapping tape 245 together comprise anelectrode stack assembly wrap which has been discovered to help preventundesired movement or shifting of electrode stack assembly 225 duringsubsequent processing. It will now become apparent to one skilled in theart that many means other than those disclosed explicitly herein existfor immobilizing and securing electrode stack assembly 225 duringsubsequent processing which accomplish substantially the same functionas the electrode stack assembly wrap comprising outer wrap 115 andwrapping tape 245. Alternative means for immobilizing and securingelectrode stack assembly 225 other than those described hereinaboveexist. Such alternative means include, but are not limited to, roboticor other mechanical clamping and securing means not necessarily forminga portion of electrode stack assembly 225, adhesive electrolytes forforming separator layers 180, and so on.

[0099] The stacking process by which electrode stack assembly 225 ismost preferably made begins by placing outer wrap 115 into a stackingfixture followed by placing outer paper or separator layer 165 athereon. Next, cathode layer 175 a is placed atop separator layer 165 a,followed by separator layers 180 a and 180 b being disposed thereon.Cold-welded anode sub-assembly 170 a is then placed atop separator layer180 b, followed by placing separator layers 180 a and 180 b thereon, andso on. The placing of alternating cathode layers 175 and anodesub-assemblies 170 with separator layers 180 a and 180 b interposedtherebetween continues in the stacking fixture until final cathode layer175 h has been placed thereon.

[0100] In the embodiment of electrode stack assembly 225 shown in FIG.6(a), eight anode sub-assemblies (anode sub-assemblies 170 a through 170h) and nine cathode layers (cathode layers 175 a through 175 i) areillustrated. The voltage developed across each combined anodesub-assembly/separator layer/cathode layer assembly disposed withinelectrode stack assembly 225 most preferably ranges between about 360and about 390 Volts DC. As described below, the various anodesub-assemblies of electrode stack assembly 225 are typically connectedin parallel electrically, as are the various cathode layers of electrodestack assembly 225.

[0101] Consistent with the discussion hereinabove concerning FIG. 4, itwill now be understood by one skilled in the art that electrode stackassembly 225 shown in FIG. 6(a) is merely illustrative, and does notlimit the scope of the present invention in any way respecting thenumber or combination of anode sub-assemblies 170, cathode layers 175,separator layers 180, anode tabs 195, cathode tabs 176, and so on. Thenumber of electrode components is instead determined according to thetotal capacitance required, the total area of each layer, the specificcapacitance of the foil employed and other factors.

[0102] In another embodiment of electrode stack assembly 225, the numberof anode layers 185 employed in each anode sub-assembly 170 is varied inthe stack. Such a design permits the fabrication of capacitors havingthe same layer area but nearly continuously varying different andselectable total capacitance that a user may determine by increasing ordecreasing the number of anode layers 185/190 included in selected anodesub-assemblies 170 (as opposed to adding or subtracting fullanode/cathode subassemblies 227 from electrode stack assembly 225 tothereby change the total capacitance). Following placing of cathodelayer 175 i in the stack, outer paper layer 165 b is placed thereon, andouter wrap 115 is folded over the top of electrode stack assembly 225.Wrapping tape 245 then holds outer wrap 115 in place and secures thevarious components of electrode stack assembly 225 together.

[0103] The physical dimensions of separator layers 165 and 180 are mostpreferably somewhat larger than those of anode sub-assemblies 170 andcathode layers 175 to prevent contact of the electrodes with the casewall or electrical shorting between opposing polarity electrode layersdue to the presence of burrs, stray or particulate material, debris orimperfections occurring therein- The reliability and functionality ofcapacitor 265 may be compromised if a portion of anode sub-assembly 170comes into contact with a conducting case wall, if a burr on theperiphery of anode sub-assembly 170 or cathode layer 175 comes intocontact with an adjoining layer of opposing polarity, or if separatorlayer 180 a or 180 b does not provide sufficient electrical insulationbetween adjoining opposite-polarity electrode layers and conductingparticulate matter bridges the gap therebetween.

[0104] The additional separator material most preferably disposed aboutthe periphery of electrode stack assembly 225 is referred to herein asseparator overhang. Decreasing the amount of separator overhangincreases the energy density of capacitor 265. It is beneficial from anenergy density optimization perspective, therefore, to decrease theamount or degree of separator overhang. The amount of separator overhangrequired has been discovered to be primarily a function of the stack-uptolerance characteristic of the stacking method employed.

[0105] A preferred method for assuring consistent registration ofseparator layers 165 and 180, anode sub-assemblies 170 and cathodelayers 175 in electrode stack assembly 225 involves stacking the variouselements of electrode stack assembly 225 using robotic assemblytechniques. More particularly, the various electrode and separatorlayers of electrode stack assembly 225 are stacked and aligned using anassembly work cell comprising four Seiko 4-axis SCARA Model No. TT8800and TT8500, or equivalent, to pick up and place the various electrodeand separator elements in an appropriate stacking fixture. Othersuitable methods for stacking and registering electrode and separatorlayers include cam driven walking beam assembly machine techniques,rotary table machine techniques, multiple station single stackingmachine techniques, and the like.

[0106] In a preferred method, a pre-formed or cut separator, electrodelayer or sub-assembly is presented to a robot arm, which then picks thepart up with end-of-arm tooling. A Venturi system produces a vacuum inthe end-of-arm tooling. The system creates a vacuum at an appropriatetime such that the part is sucked up onto the end-of-arm tooling. Thevacuum is next released when the part is placed in the stacking fixture.A direct vacuum system, such as rubber suction cups, or other contact ornon-contact pick up robotic or manual assembly methods may also beemployed. The position of the part is robotically translated from thepickup point into the stacking fixture by the robot arm with an accuracyof 0.005 inch (0.013 mm) or less. After placing the part in the stackingfixture, part alignment is most preferably verified electronically witha SEIKO COGNEX 5400 VISION System, or equivalent, in combination with aSONY XC-75 camera, or equivalent. The camera is mounted on the robot armto permit the accuracy of part placing to be verified. This system canaccurately determine the position of each part or element in electrodestack assembly 225 to within 0.01 millimeters. Once all layers have beenplaced in the stacking fixture by the robot arm, the stack is presentedfor wrapping.

[0107] The foregoing methods permit precise alignment and stacking ofseparator layers 165 and 180, anode sub-assemblies 170 and cathodelayers 175 in electrode stack assembly 225, while minimizing theaddition of undesirable unused volume to capacitor 265.

[0108] Another method for assuring registration of separator layers 165and 180, anode sub-assembly 170 and cathode layer 175 in electrode stackassembly 225 involves alignment elements disposed within the stackingfixture are employed in a manual process which utilizes fixtureregistration points. In such a method, the stacking fixture has severalalignment elements such as posts or side walls disposed about itsperiphery for positioning separator layers 165 and 180. Because cathodelayers 175 and anode sub-assemblies 170 do not extend to the peripheryof the separator, an alternative means for accurately positioning thoseelectrodes becomes necessary.

[0109] Positioning of alternating cathode layers 175 and anodesub-assemblies 170 is most preferably accomplished using alignmentelements such as posts or side walls disposed about the periphery ofcathode tab 176 and anode tab 195. It has been discovered that theaccuracy of layer placing and positioning is primarily a function of thelength of the electrode tabs. The longer the tab, the less significantthe alignment error becomes. Electrode tab length must typically bebalanced against the loss of electrode material which occurs during diecutting, which in turn results primarily due to the longer length ofcathode tab 176 in respect of the length of anode tab 195. Tabs 176 and195 may include or contain alignment features therein having anysuitable geometry for facilitating registration and positioning inrespect of alignment elements. Any additional tab length utilized forregistration of the electrode layers is most preferably trimmed fromelectrode stack assembly 225 during the process of electrode tabinterconnection (more about which we say below).

[0110] Another method for ensuring registration of separator layers 165and 180, anode sub-assembly 170 and cathode layer 175 in electrode stackassembly 225 does not require the use of internal alignment elementswithin capacitor 265 is enveloping or covering anode sub-assembly 170and cathode layer 175 with separator material. In this method, separatorlayers 180 a and 180 b are combined into a single die cut piece partthat is folded around either anode sub-assembly 170 or cathode layer175. The free edges of the separator are then secured by doubled-sidedtransfer tape, another adhesive, stitching or ultrasonic paper welding.Construction of an electrode sub-assembly in this manner secures andregisters anode sub-assembly 170 and cathode layer 175 in respect of theperiphery of the separator envelope so formed. The resultinganode/cathode sub-assembly 227 is then presented for stacking inelectrode stack assembly 225.

[0111]FIG. 7 shows a top perspective view of one embodiment of anelectrode stack assembly 225 of the electrolytic capacitor 265. FIG. 8shows an enlarged view of a portion of the electrode stack assembly 225of FIG. 7. After wrapping electrode stack assembly 225 with outer wrap115 and wrapping tape 245, interconnection of gathered anode tabs 232and gathered cathode tabs 233 with their respective external terminalsis most preferably made.

[0112]FIG. 9 shows an exploded top perspective view of the embodiment ofthe capacitor 265 employing the electrode stack assembly of FIGS. 6, 7and 8 therein and not employing a case liner. This embodiment includesanode feedthrough 120 and cathode feedthrough 125 most preferably havingcoiled basal portions 121 and 126, respectively. Feedthroughs 120 and125 provide electrical feedthrough terminals for capacitor 265 andgather gathered anode tabs 232 and gathered cathode tabs 233 withinbasal portions 121 and 126 for electrical and mechanicalinterconnection.

[0113] In one method of making tab interconnections and feedthroughterminal connections, feedthrough wire is first provided forconstruction of feedthroughs 120 and 125, as shown in FIGS. 9 and 10(a).In one embodiment, a preferred feedthrough wire is aluminum having apurity greater than or equal to 99.99% and a diameter of 0.020 inch(0.510 mm). Wire is trimmed to predetermined lengths for use in anodefeedthrough 120 or cathode feedthrough 125. One end of the trimmed wireis coiled such that its inside diameter or dimension is slightly largerthan the diameter or dimension required to encircle gathered anode tabs232 or gathered cathode tabs 233.

[0114] Gathered anode tabs 232 are next gathered, or brought together ina bundle by crimping, and inside diameter 131 of anode feedthrough coilassembly 120 is placed over gathered anode tabs 232 such that anodefeedthrough pin 130 extends outwardly away from the base of gatheredanode tabs 232. Similarly, gathered cathode tabs 233 are gathered andinside diameter 136 of cathode feedthrough coil assembly 125 is placedover gathered cathode tabs 233 such that cathode feedthrough pin 135extends outwardly away from the base of cathode tab 233. Coiled basalportions 121 and 126 of anode and cathode feedthroughs 120 and 125 arethen most preferably crimped onto anode and cathode tabs 232 and 233,followed by trimming the distal ends thereof, most preferably such thatthe crimps so formed are oriented substantially perpendicular toimaginary axes 234 and 235 of gathered anode and cathode tabs 232 and233. Trimming the distal ends may also, but less preferably, beaccomplished at other non-perpendicular angles respecting imaginary axes234 and 235.

[0115] A crimping force is applied to feedthrough coils 121 and 126 andtabs 232 and 233 throughout a subsequent preferred welding step. In onemethod, it is preferred that the crimped anode and cathode feedthroughsbe laser or ultrasonically welded along the top portion of the trimmededge of the distal ends to anode and cathode tabs 232 and 233. Followingwelding of feedthroughs 120 and 125 to gathered anode tabs 232 andgathered cathode tabs 233, respectively, pins 130 and 135 are bent forinsertion through feedthrough holes 142 and 143 of case 90.

[0116] Many different embodiments of the feedthroughs, and means forconnecting the feedthroughs to anode and cathode tabs exist other thanthose shown explicitly in the figures. For example, the feedthroughsinclude embodiments comprising basal portions having open sides, forming“U” or “T” shapes in cross-section, forming a coil having a single turnof wire, forming a coil having three or more turns of wire, formed fromflattened wire, or basal portions formed from crimping sleeves or layersof metal for connecting feedthrough pins 130 and 135 to anode andcathode tabs 232 and 233. Various methods of making tab interconnectionsand feedthrough connections which are not critical to the presentinvention are disclosed in commonly assigned U.S. Pat. No. 6,006,133which may be followed in completing the fabrication of capacitor 265.

[0117]FIG. 10(a) shows an exploded top perspective view of capacitor 265of FIG. 9 in a partially assembled state. Case 90 contains a means foraccepting anode ferrule 95 therein, shown in FIGS. 9 and 10(a) as anodefeedthrough hole or opening 142. Case 90 further contains a means foraccepting cathode ferrule 100, shown in FIGS. 9 and 10(a) as cathodefeedthrough hole or opening 143. Case 90 also includes a means foraccepting fill port ferrule 105, shown in FIGS. 9 and 10(a) as fill porthole 139. In a preferred embodiment, case 90 and cover 110 are formed ofaluminum and are electrically connected to the cathode layers, and wherecase 90 and cover 110 are at the same electrical potential as thecathode layers, i.e., at negative potential.

[0118] Ferrules 95, 100 and 105 are most preferably welded to case 90(or otherwise attached thereto such as by a suitable epoxy, adhesive,solder, glue or the like), and together comprise case sub-assembly 108.Radial flanges in anode ferrule 95 and cathode ferrule 100 provide aregion for making a lap joint between the side wall of case 90 andaround the perimeters of feedthrough ferrule holes 142 and 143. Inpreferred methods, a circumferential laser weld is made in thecircumferential joint between the ferrules and the case side wall 92,and welding is carried out in two primary steps. First, a series of tackwelds is made around the circumference of the joint. The tack welds aremost preferably made either by making adjoining, successive tack weldsaround the perimeter or by making a first tack weld at a first locationalong the perimeter, making a second weld diametrically opposed from thefirst weld along the perimeter, making a third weld adjacent to thefirst weld, making a fourth weld adjacent to the second weld, and so on.Finally, a final closing weld is made around the hole perimeter tohermetically seal tack welded joint 93.

[0119] Wire guides 140 and 141 center pins within the inside diameter ofthe ferrules to permit anode and cathode pins 130 and 135 to beelectrically insulated from the inside surface of case 90, anode ferrule95, and cathode ferrule 100. Wire guides 140 and 141 may themselves beelectrically insulating, and electrical insulation of pins 130 and 135from case 90 and other components is most preferably enhanced by meansof potting adhesive 160.

[0120] Wire guides 140 and 141 most preferably contain annular, ramped,or “snap-in” features formed integrally therein. Those features preventwire guides 140 and 141 from being pushed out of their respectiveferrules during handling, but are most preferably formed such thatinsertion of wire guides 140 and 141 in their corresponding ferrules mayoccur using forces sufficiently low so as not to damage case 90 orferrules 95 or 100 during the inserting step.

[0121] Wire guides 140 and 141 may be formed from any of a wide varietyof electrically insulating materials that are stable in the environmentof an electrolytic capacitor. In one preferred embodiment, the materialfrom which wire guides 140 and 141 is made is an injection moldedpolysulfone known as AMOCO UDEL supplied by Amoco Performance Productsof Atlanta, Ga. In other embodiments, wire guides 140 and 141 may beformed from other chemically resistant polymers such as fluoroplastics(e.g., ETFE, PTFE, ECTFE, PCTFE, FEP, PFA or PVDF), fluoroelastomers,polyesters, polyamides, polyethylenes, polypropylenes, polyacetals,polyetherketones, polyarylketones, polyether sulfones, polyphenylsulfones, polysulfones, polyarylsulfones, polyetherimides, polyimides,poly(amide-imides), PVC, PVDC-PVC copolymers, CPVC, polyfurans,poly(phenylene sulfides), epoxy resins, silicone elastomers, nitrilerubbers, chloroprene polymers, chlorosulfonated rubbers, polysulfiderubbers, ethylene-polypropylene elastomers, butyl rubbers, polyacrylicrubbers, fiber-reinforced plastics, glass, ceramic and other suitableelectrically insulating, chemically compatible materials.

[0122] As used in the specification and claims hereof, the foregoingacronyms have the following meanings: the acronym “ETFE” meanspoly(ethylene-co-tetrafluoroethylene); the acronym “PTFE” meanspolytetrafluoroethylene; the acronym “CTFE” meanspoly(ethylene-co-chlorotrifluoroethylene); the acronym “PCTFE” meanspolychlorotrifluoroethylene, the acronym “FEP” means fluorinatedethylene-propylene copolymer; the acronym “PFA” perfluoroalkoxyfluoropolymer; the acronym “PVDF” means polyvinylidene fluoride; theacronym “PVC” means polyvinyl chloride; the acronym “PVDC-PVC” meanspolyvinylidene chloride—polyvinyl chloride copolymer; and the acronym“CPVC” means chlorinated polyvinyl chloride.

[0123] A preferred material for forming connector block 145 is aninjection molded polysulfone known as AMOCO UDEL supplied by AmocoPerformance Products of Atlanta, Ga. Connector block 140 may also beformed from any suitable chemically resistant thermoplastic polymerssuch as a fluoroplastic (e.g., ETFE, PTFE, ECTFE, or PCTFE, FEP, PFA,PVDF), polyester, polyamide, polyethylene, polypropylene, polyacetal,polyarylketone, polyether sulfone, polyphenyl sulfone, polysulfone,polyarylsulfone, polyetherimides, polyimide, poly(amide-imide), PVC,PVDC-PVC copolymer, CPVC, polyfuran, poly(phenylene sulfide), epoxyresin and fiber reinforced plastic.

[0124] In one embodiment, connector block 145 is placed on anode ferrule95 and cathode ferrule 100 by guiding anode feedthrough pin 130 throughconnector block anode feedthrough hole 300, and then guiding cathodefeedthrough pin 135 through connector block cathode feedthrough hole305. Connector block 145 is next seated flush against the exteriorsurface of case 90. Anode feedthrough pin 130 is then inserted intoanode crimp tube 150 b of wire harness 155. Cathode feedthrough pin 135is then inserted into cathode crimp tube 150 a of wire harness 155.Crimp tubes 150 a and 150 b are then crimped to feedthrough pins 130 and135.

[0125] In other preferred embodiments, electrical connections inconnector block 145 may be established using techniques such asultrasonic welding, resistance welding and laser welding. In suchjoining techniques, the joint geometry may also be a cross-wire weldbetween feedthrough wire 130 or 135 and harness wire 151 or 152.

[0126] The distal or basal portions of crimp tubes 150 a and 150 b arecrimped on insulated anode lead 151 and insulated cathode lead 152,respectively. Insulated leads 151 and 152 are likewise connected toterminal connector 153. Terminal connector 153 may most preferably beconnected to electronics module 360. Standard methods of making aluminumelectrolytic capacitors do not lend themselves readily to very smallcrimp connections, especially in miniaturized ICD designs. A preferredmethod permits small crimp connections and interconnection means to beformed, and further permits highly efficient packaging in ICD IPG 10.

[0127] In the preferred method described above, connector block 145 andepoxy adhesive provide strain relief to feedthrough pins 130 and 135 andto the feedthrough wire crimp connections, and further provide an epoxyseal between wire guides 140 and 141, case 90 and ferrules 95 and 100.The crimp tubes may also serve as a connection point for device levelassembly. Alternatively, the crimp tubes may be integrated within wireharness 155 prior to capacitor assembly. The wire harness may then serveas a means of routing capacitor electrical connections as desired in,for example, device level assembly steps. In the embodiment shown inFIGS. 10 and 11, terminal connector 153 forms the female end of a slidecontact. In another embodiment, terminal connector 153 is connected toother modules by resistance spot welding, ultrasonic wire bonding,soldering, crimping, or other attachment means.

[0128] The particular configuration and fabrication of the feedthroughs,the connections thereto, the connector block, the wire harness, etc.,are not important to the present invention. Further details related tothe fabrication of the depicted, exemplary form of the feedthroughs,internal and external connections thereto, the connector block, the wireharness, etc., are set forth in detail in the above-referenced '133patent.

[0129]FIG. 11 shows a top view of one embodiment of assembled capacitor265 with cover 110 not present and without a case liner separatingelectrode stack assembly 225 from the case 90 and cover 110. In oneembodiment, the head space portion of electrode stack assembly 225(referred to herein as head space 230) is insulated from case 90 andcover 110. The means by which head space insulation may be providedinclude molded, thermally-formed, die cut, or mechanically formedinsulating materials and means, where the materials and means are stablein the environment of an electrolytic capacitor. Suitable materials fromwhich head space insulators may be formed include all those listedhereinabove respecting materials for forming wire guides 140 and 141.Another means of providing head space insulation is to wrap electricallyinsulating tape, similar to wrapping tape 245, around head space 230 toprevent the anode or cathode terminals from contacting case 90 or cover110 or each other. Various crimp and joint configurations for joiningthe cover 110 to case 90 are described in detail in theabove-referenced, commonly assigned '133 patent. In accordance with oneaspect of the present invention, the head space insulation may beprovided by a case liner 300 described further below. FIG. 11 may alsoinclude a lower half section 310 of the case liner 300 described below(not visible in FIG. 11) that the electrode stack assembly 225 is nestedinto. An upper half section would be fitted over the electrode stackassembly after completion of the above-described electrical connectionsfor connecting feedthrough pins 130 and 135 to anode and cathode tabs232 and 233.

[0130] After all welding steps are completed, the interior case chamberof capacitor 265 is filled with electrolyte through fill port 107 weldedinto a hole 139 in the side wall of the capacitor case 90, the capacitoris aged, the fill port lumen is closed and the capacitor is tested. Thecapacitor aging, the fill port construction, use in filling thecapacitor interior case with electrolyte and the closure of the fillport lumen are not critical to the present invention, and examples ofthe same are disclosed in detail in the above-referenced, commonlyassigned '133 patent. Applications in implantable defibrillators mayrequire two capacitors 265 to be connected in series. In thisembodiment, an insulator is provided by a two sided adhesive beingdisposed between the capacitors 265 so that they are joined alongopposing faces with the insulator/adhesive strip disposed therebetween.The pair of capacitors 265 is then provided for assembly in ICD IPG 10as shown and described above with respect to FIGS. 3(a) through 3(g).

[0131] In accordance with one aspect of the present invention, thecapacitor case sub-assembly 108 and the case cover 110 of FIGS. 9 and10(a) define an interior case chamber 93 when hermetically weldedtogether at the case side wall upper edge as described above. The case90 has a base 96 bounded by a base peripheral edge at the junction ofthe base 96 and side wall 91 extending upwardly at a right angletherefrom to a case opening edge 94 for receiving cover 110 whereby theinterior case chamber has a case chamber periphery 97 corresponding inshape to the base peripheral edge 93 and bounded by the interior caseside wall surface 92.

[0132]FIG. 10 (b) illustrates details and dimensions of the case sidewall 91 between the base 96 and the upper side wall edge 94 thatreceives the cover 110, particularly the side wall inner surface 92 thatbounds and defines the case periphery, and the case height H_(cw) andstack tolerance t_(o). The number N of capacitor layers and the overallelectrode stack assembly thickness or stack height H_(N) of the Nstacked capacitor layers that are fitted into the interior case chamber93 depends on the specified case side wall height H_(cw), and the stackheight tolerance t_(o). The stack tolerance t_(o) is defined to ensurethat the electrode stack assembly 225, with or without a liner, fitsinto the interior case chamber 93 after assembly and to allow forseparator swelling upon filling with electrolyte and case swelling dueto release of gases during charging and discharging cycles. A case liner300 as shown in FIGS. 14 and 15 can also be disposed around theelectrode stack assembly periphery 226, and its upper and lower wallthicknesses are taken into account in specifying the stack heighttolerance t_(o).

[0133] The electrode stack assembly 225 located within the interior casechamber 93 is dimensioned to have a stack periphery 226 configured inmating relation with the case chamber periphery defined by the interiorcase side wall surface 92 as shown in FIGS. 10(a), 11, and 13. Theparticular exemplary embodiment described above in reference to aparticular electrode stack assembly 225 has h capacitor layers 227 a-227h (N=h) sandwiched between lower and upper separator layers 165 a and165 b. The capacitor layers 227 a-227 h and separator layers 165 a and165 b are stacked in registration upon one another and between the casebase 96 and the cover 110 through a stack height H_(h). For convenience,that example will be followed in the discussion of FIG. 13 which depictsedge portions of a first group of N₁ capacitor layers each having afirst capacitor layer thickness T_(CL1) and a second group of N₂capacitor layers each having a first capacitor layer thickness T_(CL2).It will be understood that the first group of N₁ capacitor layerscomprises capacitor layers 227 a through 227 d having a total layerthickness of 4 * T_(CL1) and a second group of N₂ capacitor layers 227 ethrough 227 h having a total layer thickness of 4 * T_(CL2). The totalstack height H_(N)=4 * T_(CL1)+4 * T_(CL2) (plus the thicknesses of theupper and lower separator layers 165 a and 165 b, if present).

[0134] As described above with respect to FIG. 4, and as shown in FIG.13, each capacitor layer 227 a-227 h comprises a cathode layer 175 a-175h having a cathode peripheral edge 175 a′-175 h′ extending toward theinterior case side wall 92 throughout a major portion 229 of the casechamber periphery 97 (shown in FIG. 11) and having a cathode tab 176a-176 h extending in the head space 230 toward the case side wall 92 ina minor portion 231 of the case chamber periphery 97. Thus, the stackperiphery 226 similarly consists of a major periphery length 229corresponding to major portion 229 and a minor periphery length 241corresponding to minor portion 231 at the head space 230 as shown inFIGS. 7 and 8. The stack periphery 226 is closely spaced from andconfigured in shape through the major periphery length 228 to the shapeof the major portion 229 of the case chamber periphery 97.

[0135] Each capacitor layer 227 a-227 h also includes an anodesub-assembly 170 a-170 h comprising at least one anode layer 185 and/or190 having an anode sub-assembly peripheral edge 170 a′-170 h′ extendingtoward the case side wall 92 throughout the major portion 229 and havingan anode tab 195 a-195 h extending in the head space 230 toward the caseside wall interior surface 92 in the minor portion 231 of the casechamber periphery 97.

[0136] In accordance with the teachings of the present invention, theanode sub-assemblies of the N₁ capacitor layers (227 c and 227 d in FIG.13) comprise x anode layers (where x=3 in FIG. 13) each having an anodelayer thickness t_(x) that are stacked together, whereby each anodesub-assembly (170 c and 170 d in FIG. 13) has an anode sub-assemblythickness T_(x). Similarly, the anode sub-assemblies of the N₂ capacitorlayers (227 e and 227 f in FIG. 13) comprises y anode layers (where y=4in FIG. 13) each having an anode layer thickness t_(y) that are stackedtogether, whereby each anode sub-assembly (170 e and 170 f in FIG. 13)has an anode sub-assembly thickness T_(y).

[0137] In one thickness tailoring embodiment, the x anode layers eachhave the same anode layer thickness t_(x), the y anode layers each havethe same anode layer thickness t_(y), t_(x)=t_(y) and therefore thecondition x≠y is necessary in order to achieve differing anodesub-assembly thicknesses T_(x) and T_(y). In a second tailoringembodiment, the x anode layers each have the same anode layer thicknesst_(x), the y anode layers each have the same anode layer thicknesst_(y), but t_(x)≠t_(y), and therefore either condition x≠y or x=y issufficient in order to achieve differing anode sub-assembly thicknessesT_(x) and T_(y). In a third tailoring embodiment, certain or all of thex anode layers have differing anode layer thicknesses t_(x1), t_(x2), etseq., and certain or all of the y anode layers have differing anodelayer thicknesses t_(y1), t_(y2), et seq., and t_(x1)≠t_(ty1),t_(x2)≠t_(y2), et seq., and therefore either condition x≠y or x=y issufficient in order to achieve differing anode sub-assembly thicknessesT_(x) and T_(y). In a fourth tailoring embodiment, certain or all of thex anode layers have differing anode layer thicknesses t_(x1), t_(x2), etseq., and certain or all of the y anode layers have differing anodelayer thicknesses t_(y1), t_(y2), et seq., and t_(x1)=t_(y1),t_(x2)=t_(y2), et seq., and therefore the condition x≠y is necessary inorder to achieve differing anode sub-assembly thicknesses T_(x) andT_(y).

[0138] Each capacitor layer 227 a-227 h also includes the electrolytebearing inner separator layer 180 formed of two separator layer sheets180 a and 180 b as depicted in FIGS. 4 and 13.

[0139] Each separator layer 180 has a separator peripheral edge 180′extending toward the interior case side wall 92. The separator layers180 disposed between each adjacent anode sub-assembly and cathode layerelectrically separates each anode sub-assembly from each adjacentcathode layer of the stacked capacitor layers. The upper and lowerseparator layers 165 a and 165 b of FIGS. 9 and 10(a) may also beapplied to the upper and lower surfaces of the electrode stack assembly225.

[0140] Thus, the total electrode stack assembly thickness or heightH_(N) is dependent upon the total number N of capacitor layers and thethickness T₁, T₂, . . . T_(n) of the selected groups N₁, N₂, . . . N_(n)of capacitor layers (and the thicknesses of the upper and lowerseparator layers 165 a and 165 b, if present). The capacitor layerthickness T₁, T₂, . . . T_(n) depends on the number and the thickness ofthe anode foils or sheets of the anode layers, the thickness of thecathode layers, and the thickness of the separator sheets, particularlywhen swollen by liquid electrolyte. By this selection, the maximumsurface area and capacitance of the electrode stack assembly is achievedand empty height space of the interior case chamber is minimized withoutcausing undue pressure.

[0141] As noted earlier, the principles of the present invention may beapplied to any case enclosure configuration wherein the total electrodestack assembly thickness or height H_(N) is correlated with the caseheight H_(cw) which may correspond to a case width or thickness in thesituation where the cover is on an end or side of the enclosure ratherthan the top as illustrated in the figures and described above.

[0142] In further reference to the embodiment of FIG. 13, it ispreferred to cut or otherwise form separator layer 180 such that itsouter periphery edge 180′ is the outermost surface of the stackperiphery 226 and conforms closely to that of the case chamber periphery97 so that the outer peripheral edges 180′ contact the adjacent interiorside wall surface 92 In preferred embodiments, the periphery ofseparator layer is disposed within±0.009 inches of the adjoining sidewall surface 92. Such close conformity between the periphery edge 180′and the corresponding internal side walls of case 90 has been discoveredto provide the advantage of permitting separator layers 180 toimmobilize or secure firmly in place electrode stack assembly 225 incase 90. This immobilization occurs because the separator paper formingseparator layers 180 swells after electrolyte is added through the lumenof fill port 107 into the interior case chamber 93 of the otherwiseassembled and sealed capacitor 265.

[0143] Further in reference to FIG. 13, in each capacitor layer 227 b,227 c, et seq., the anode sub-assembly peripheral edges 170 b′, 170 c′,et seq., are disposed at a first distance D1 from the separator layerperipheral edges 180′ and the case interior side wall surface 92throughout the major portion 229 of the case chamber periphery 97. Thecathode peripheral edges 175 a′, 175 b′, 175 c′, et seq., are disposedat a second distance D2 from the case interior side wall surface 92 andthe separator layer peripheral edges 180′ throughout the major portion229 of the case chamber periphery 97. The distances D1 and D2 can be thesame as illustrated, or the distance D2 can be greater than the distanceD1, thereby increasing anode surface area and locating the anodeperipheral edges such that anode sub-assembly peripheral edges theycontact one another if edge defects are present and do not electricallyshort against an intervening cathode layer.

[0144]FIG. 14 shows a top view of such an embodiment of assembledcapacitor 265 with cover 110 not present and with a case liner 300separating electrode stack assembly 225 from the case 90 and cover 110.The case liner 300 provides an insulating barrier positioned aboutelectrode stack assembly 225 to cover the stack periphery 226 throughoutthe major portion 229 illustrated in FIG. 9 and to also cover an edgeportion of the outer separator layers 165 a and 165 b. Wiring harnessconnector block 145 is coupled to the electrode stack 108 through case90 as described above.

[0145]FIG. 15 illustrates case liner 300 as used in FIG. 14 to encloseelectrode stack assembly 225. In this illustrated embodiment, case liner300 is constructed in an upper half section 308 and a lower half section310. Electrode stack assembly 225 is positioned within the upper andlower half sections 308 and 310 in the assembly depicted in FIG. 15. Acase liner side wall 306 that extends throughout the major portion 229illustrated in FIG. 9 is formed when the assembly depicted in FIG. 15 iscompleted. A cut out section 312 is made in the case liner side wall 306in the minor portion 231 of the case chamber periphery 97 shown in FIG.11 to facilitate electrical connections from the feedthrough pins 130and 135 to anode and cathode tabs 232 and 233, respectively. Theelectrical connections are made after the liner lower half section 310is placed in the interior case chamber 93 and the electrode stackassembly is nested into the lower half section as in FIG. 11. Theelectrical connections illustrated in FIGS. 9, 10(a) and-11 arecompleted, and the upper case liner half section 308 is placed over theupper surface of the electrode stack assembly. A further cut-out hole isprovided in the upper and lower half sections 308 and 310 in alignmentwith the fill port 107 to allow leak testing and introduction of theelectrolyte as described, for example, in the above-referenced '133patent.

[0146] Case liner 300 is made of an appropriate thickness ofelectrically insulating material depending upon the mechanical design ofelectrode stack assembly 225, the amount of separator layer overhang,the desired distance D1 separation between electrode stack periphery 226and the case side wall surface 92, etc. In one embodiment liner wallthickness is in the range of 0.001 to 0.10 inches (0.025 to 0.254 mm)and more preferably in the range of 0.003 to 0.005 inches (0.075 to0.127 mm). Liner wall thickness is also a function of the type ofinsulating material from which liner 300 is made.

[0147] In one embodiment, liner 300 is made of a polymeric material orpolymeric blend of materials, and in one preferred embodiment thepolymeric material is polysulfone. Other suitable polymeric materialsinclude polypropylene, polyethylene and ETFE. Optionally, liner 300 canbe formed of other insulating materials, such as those materialspreviously disclosed herein for construction of the wire guides 140 and141. Liner 300 acts as a separator between the electrode stack periphery226 and case side wall surface 92, and therefore could be made of porousmaterials or made porous, e.g., by having holes therethrough. Othersuitable electrical non-conducting materials for liner 300 will becomeapparent to those skilled in the art after reading the presentapplication.

[0148] The mechanical design of the liner 300 may take many differentconfigurations depending upon the configuration of the electrode stackassembly 225. In applications where the desired shape of capacitorassembly 64 has a low thickness to width aspect ratio, a stacked plateelectrode 108 design is preferred to achieve optimal energy density.Liner 300 can be constructed of a single part, a two part assembly, oroptionally made with multiple component construction. Variousembodiments of liner 300 mechanical design are described in detail laterin commonly assigned, co-pending U.S. patent application Ser. No.09/531,352 filed Mar. 20, 2000, in the names of Mark D. Breyen et al.,and entitled IMPLANTABLE MEDICAL DEVICE HAVING A CAPACITOR ASSEMBLY WITHLINER. The use of liner 300 extends to cylindrical or other capacitorassembly 64 shapes. Although liner 300 is preferably thermoformed ormolded, in another preferred embodiment liner 300 can be coated ordeposited on the inside of case 100 or upon electrode stack assembly225. In this embodiment, the liner 300 is preferably less than 0.050inch (0.130 mm) and more preferably less than 0.001 inches (0.025 mm),and more preferably less than 0.0005 inches (0.0013 mm) thick.

[0149] Although only a few exemplary embodiments of a capacitor 265 inwhich the present invention is advantageously implemented have beendescribed in detail above, those skilled in the art will appreciatereadily that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the invention. Accordingly, all such modifications areintended to be included within the scope of the present invention asdefined in the following claims.

[0150] The preceding specific embodiments are illustrative of acapacitor structure and method of fabrication thereof and itsincorporation into an IMD in accordance with preferred embodiments ofthe present invention. It is to be understood, therefore, that otherexpedients known to those skilled in the art or disclosed herein, andexisting prior to the filing date of this application or coming intoexistence at a later time may be employed without departing from theinvention or the scope of the appended claims. In the claims,means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

[0151] All patents and printed publications disclosed herein are herebyincorporated by reference herein into the specification hereof, each inits respective entirety.

We claim:
 1. An implantable medical device comprising: a housing; an electronics module disposed within the housing; an energy source within the housing electrically coupled to the electronics module; a capacitor assembly within the housing electrically coupled to the electronics module, the capacitor further comprising: a sealed capacitor case defining an interior case chamber, the case having a base having a base peripheral edge, a case side wall extending between the base peripheral edge through a side wall height to a side wall opening edge defining a case opening edge and a case chamber height H_(cw); a cover adapted to be sealed against the case opening edge to enclose an interior case chamber, whereby the interior case chamber has a case chamber periphery defined by said case side wall; and an electrode stack assembly located within the interior case chamber, the electrode stack assembly having a stack periphery configured in mating relation with the case chamber periphery and further comprising a plurality of N capacitor layers stacked in registration upon one another and between the case base and the cover through a stack height H_(N) selected to be equal to or less than the case chamber height H_(cw) by a predetermined tolerance, wherein N₁ capacitor layers of the N capacitor layers each have a first capacitor layer thickness T_(CL1) and N₂ capacitor layers of the N capacitor layers each have a second capacitor layer thickness T_(CL2), whereby the stack height H_(N) is dependent upon N₁*T_(CL1)+N₂*T_(CL2).
 2. An implantable medical device comprising: a housing; an electronics module disposed within the housing; an energy source disposed within the housing and electrically coupled to the electronics module; and a capacitor assembly disposed within the housing and electrically coupled to the electronics module, the capacitor assembly further comprising: a sealed capacitor case defining an interior case chamber, the case having a base having a base peripheral edge, a case side wall extending between the base peripheral edge to a side wall opening edge defining a case opening edge, and a cover sealed against the case opening edge to enclose the interior case chamber, whereby the interior case chamber has a case chamber periphery and a case chamber height H_(cw); and an electrode stack assembly located within the interior case chamber comprising N capacitor layers stacked in registration upon one another and between the case base and the cover having a stack height H_(N) selected to be equal to or less than the case chamber height H_(cw) by a predetermined tolerance, wherein N₁ capacitor layers of the N capacitor layers each have a first capacitor layer thickness T_(CL1) and each further comprise: a cathode layer having a cathode layer thickness and a cathode peripheral edge extending toward the case side wall throughout a major portion of said case chamber periphery and having a cathode tab extending toward the case side wall in a minor portion of said case chamber periphery; an anode sub-assembly comprising x anode layers each having anode layer thickness t_(x) and an anode layer peripheral edge extending toward the case side wall throughout a major length of said base peripheral edge, whereby each anode sub-assembly has an anode sub-assembly thickness T_(x) and further comprises an anode tab extending toward the case side wall in a minor portion of said case chamber periphery; and a plurality of electrolyte bearing separator layers each having a separator peripheral edge extending toward the case side wall, the electrolyte bearing separator layers disposed on each side of the anode sub-assembly and the cathode layer of the capacitor layer, whereby the first capacitor layer thickness T_(CL1) is dependent upon the thickness of the plurality of separator layers, the cathode layer thickness and the anode sub-assembly thickness T_(x); and wherein N₂ of the N capacitor layers each have a second capacitor layer thickness T_(CL2) and each comprise: a cathode layer having a cathode layer thickness and a cathode peripheral edge extending toward the case side wall throughout a major portion of said case chamber periphery and having a cathode tab extending toward the case side wall in a minor portion of said case chamber periphery; an anode sub-assembly comprising y anode layers each having anode layer thickness t_(y) and an anode layer peripheral edge extending toward the case side wall throughout a major length of said base peripheral edge, whereby each anode sub-assembly has an anode sub-assembly thickness T_(y) and further comprises an anode tab extending toward the case side wall in a minor portion of said case chamber periphery; and a plurality of electrolyte bearing separator layers each having a separator peripheral edge extending toward the case side wall, the electrolyte bearing separator layers disposed on each side of the anode sub-assembly and the cathode layer of the capacitor layer, whereby the first capacitor layer thickness T_(CL1) is dependent upon the thickness of the plurality of separator layers, the cathode layer thickness and the anode sub-assembly thickness T_(x); and whereby the stack height H_(N) is dependent upon N₁*T_(CL1)+N₂*T_(CL2).
 3. The implantable medical device of claim 2, wherein the number x anode layers is not equal to the number y anode layers.
 4. The implantable medical device of claim 2, wherein the anode layer thickness t_(x) is equal to the anode layer thickness t_(y), and the number x anode layers is not equal to the number y anode layers.
 5. The implantable medical device of claim 4, wherein the x anode layers comprise at least two anode layers and the y anode layers exceed the number of x anode layers.
 6. The implantable medical device of claim 2, wherein the anode layer thickness t_(x) is not equal to the anode layer thickness t_(y), and the number x anode layers is not equal to the number y anode layers.
 7. The implantable medical device of claim 2, wherein the anode layer thickness t_(x) is not equal to the anode layer thickness t_(y), and the number x anode layers is equal to the number y anode layers.
 8. The implantable medical device of claim 2, wherein certain or all of the x anode layers have differing anode layer thicknesses t_(x1), t_(x2), et seq., and certain or all of the y anode layers have differing anode layer thicknesses t_(y1), t_(y2), et seq., wherein t_(x1)≠t_(y1), t_(x2)≠t_(y2), et seq., and therefore either condition x≠y or x=y is sufficient in order to achieve differing anode sub-assembly thicknesses T_(x) and T_(y).
 9. The implantable medical device of claim 2, wherein certain or all of the x anode layers have differing anode layer thicknesses t_(x1), t_(x2), et seq., and certain or all of the y anode layers have differing anode layer thicknesses t_(y1), t_(y2), et seq., wherein t_(x1)=t_(y1), t_(x2)=t_(y2), et seq., and therefore the condition x≠y is necessary in order to achieve differing anode sub-assembly thicknesses T_(x) and T_(y).
 10. An electrolytic capacitor comprising: a sealed capacitor case defining an interior case chamber, the case having a base having a base peripheral edge, a case side wall extending between the base peripheral edge through a side wall height to a side wall opening edge defining a case opening edge and a case chamber height H_(cw); a cover adapted to be sealed against the case opening edge to enclose an interior case chamber, whereby the interior case chamber has a case chamber periphery defined by said case side wall; and an electrode stack assembly located within the interior case chamber, the electrode stack assembly having a stack periphery configured in mating relation with the case chamber periphery and further comprising a plurality of N capacitor layers stacked in registration upon one another and between the case base and the cover through a stack height H_(N) selected to be equal to or less than the case chamber height H_(cw) by a predetermined tolerance, wherein N₁ capacitor layers of the N capacitor layers each have a first capacitor layer thickness T_(CL1) and N₂ capacitor layers of the N capacitor layers each have a second capacitor layer thickness T_(CL2), whereby the stack height H_(N) is dependent upon N₁*T_(CL1)+N₂*T_(CL2).
 11. An electrolytic capacitor assembly comprising: a sealed capacitor case defining an interior case chamber, the case having a base having a base peripheral edge, a case side wall extending between the base peripheral edge to a side wall opening edge defining a case opening edge, and a cover sealed against the case opening edge to enclose the interior case chamber, whereby the interior case chamber has a case chamber periphery and a case chamber height H_(cw); and an electrode stack assembly located within the interior case chamber comprising N capacitor layers stacked in registration upon one another and between the case base and the cover having a stack height H_(N) selected to be equal to or less than the case chamber height H_(cw) by a predetermined tolerance, wherein N₁ capacitor layers of the N capacitor layers each have a first capacitor layer thickness T_(CL1) and each further comprise: a cathode layer having a cathode layer thickness and a cathode peripheral edge extending toward the case side wall throughout a major portion of said case chamber periphery and having a cathode tab extending toward the case side wall in a minor portion of said case chamber periphery; an anode sub-assembly comprising x anode layers each having anode layer thickness t_(x) and an anode layer peripheral edge extending toward the case side wall throughout a major length of said base peripheral edge, whereby each anode sub-assembly has an anode sub-assembly thickness T_(x) and further comprises an anode tab extending toward the case side wall in a minor portion of said case chamber periphery; and a plurality of electrolyte bearing separator layers each having a separator peripheral edge extending toward the case side wall, the electrolyte bearing separator layers disposed on each side of the anode sub-assembly and the cathode layer of the capacitor layer; whereby the first capacitor layer thickness T_(CL1) is dependent upon the thickness of the plurality of separator layers, the cathode layer thickness and the anode sub-assembly thickness T_(x); and wherein N₂ of the N capacitor layers each have a second capacitor layer thickness T_(CL2) and each comprise: a cathode layer having a cathode layer thickness and a cathode peripheral edge extending toward the case side wall throughout a major portion of said case chamber periphery and having a cathode tab extending toward the case side wall in a minor portion of said case chamber periphery; an anode sub-assembly comprising y anode layers each having anode layer thickness t_(y) and an anode layer peripheral edge extending toward the case side wall throughout a major length of said base peripheral edge, whereby each anode sub-assembly has an anode sub-assembly thickness T_(y) and further comprises an anode tab extending toward the case side wall in a minor portion of said case chamber periphery; and a plurality of electrolyte bearing separator layers each having a separator peripheral edge extending toward the case side wall, the electrolyte bearing separator layers disposed on each side of the anode sub-assembly and the cathode layer of the capacitor layer; whereby the first capacitor layer thickness T_(CL1) is dependent upon the thickness of the plurality of separator layers, the cathode layer thickness and the anode sub-assembly thickness T_(x); and whereby the stack height H_(N) is dependent upon N₁*T_(CL1)+N₂*T_(CL2).
 12. The capacitor of claim 11, wherein the number x anode layers is not equal to the number y anode layers.
 13. The capacitor of claim 11, wherein the anode layer thickness t_(x) is equal to the anode layer thickness t_(y), and the number x anode layers is not equal to the number y anode layers.
 14. The capacitor of claim 13, wherein the x anode layers comprise at least two anode layers and the y anode layers exceed the number of x anode layers.
 15. The capacitor of claim 11, wherein the anode layer thickness t_(x) is not equal to the anode layer thickness t_(y), and the number x anode layers is not equal to the number y anode layers.
 16. The capacitor of claim 11, wherein the anode layer thickness t_(x) is not equal to the anode layer thickness t_(y), and the number x anode layers is equal to the number y anode layers.
 17. The capacitor of claim 11, wherein certain or all of the x anode layers have differing anode layer thicknesses t_(x1), t_(x2), et seq., and certain or all of the y anode layers have differing anode layer thicknesses t_(y1), t_(y2), et seq., wherein t_(x1)≠t_(y1), t_(x2)≠t_(y2), et seq., and therefore either condition x≠y or x=y is sufficient in order to achieve differing anode sub-assembly thicknesses T_(x) and T_(y).
 18. The capacitor of claim 11, wherein certain or all of the x anode layers have differing anode layer thicknesses t_(x1), t_(x2), et seq., and certain or all of the y anode layers have differing anode layer thicknesses t_(y1), t_(y2), et seq., wherein t_(x1)=t_(y1), t_(x2)=t_(y2), et seq., and therefore the condition x≠y is necessary in order to achieve differing anode sub-assembly thicknesses T_(x) and T_(y).
 19. A method of assembling an implantable medical device comprising: providing a housing; disposing an electronics module within the housing; disposing an energy source within the housing; electrically coupling the energy source to the electronics module; forming a capacitor assembly through the steps of: providing a sealed capacitor case defining an interior case chamber, the case having a base having a base peripheral edge, a case side wall extending between the base peripheral edge through a side wall height to a side wall opening edge defining a case opening edge and a case chamber height h_(cw); providing a cover adapted to be sealed against the case opening edge to enclose the interior case chamber, whereby the interior case chamber has a case chamber periphery defined by said case side wall; and forming an electrode stack assembly adapted to be located within the interior case chamber, the electrode stack assembly having a stack periphery configured in mating relation with the case chamber periphery and further comprising a plurality of N capacitor layers stacked in registration upon one another and between the case base and the cover through a stack height H_(N) selected to be equal to or less than the case chamber height H_(cw) by a predetermined tolerance, wherein N₁ capacitor layers of the N capacitor layers each have a first capacitor layer thickness T_(CL1) and N₂ capacitor layers of the N capacitor layers each have a second capacitor layer thickness T_(CL2), whereby the stack height H_(N) is dependent upon N₁*T_(CL1)+N₂*T_(CL2); disposing the electrode stack assembly in the interior case chamber; hermetically sealing the case cover to the side wall opening edge; disposing the capacitor assembly within the housing; and electrically coupling the capacitor assembly to the electronics module.
 20. The method of claim 19 wherein the step of forming an electrode stack assembly further comprises: forming the N₁ capacitor layers each having a first capacitor layer thickness T_(CL1) by: forming a cathode layer having a cathode layer thickness and a cathode peripheral edge extending toward the case side wall throughout a major portion of said case chamber periphery and having a cathode tab extending toward the case side wall in a minor portion of said case chamber periphery; forming an anode sub-assembly comprising x anode layers each having anode layer thickness t_(x) and an anode layer peripheral edge extending toward the case side wall throughout a major length of said base peripheral edge, whereby each anode sub-assembly has an anode sub-assembly thickness T_(x) and further comprises an anode tab extending toward the case side wall in a minor portion of said case chamber periphery; and disposing a plurality of electrolyte bearing separator layers each having a separator peripheral edge extending toward the case side wall on each side of the anode sub-assembly and the cathode layer of the capacitor layer; and forming the N₂ capacitor layers each having a first capacitor layer thickness T_(CL2) by: forming a cathode layer having a cathode layer thickness and a cathode peripheral edge extending toward the case side wall throughout a major portion of said case chamber periphery and having a cathode tab extending toward the case side wall in a minor portion of said case chamber periphery; forming an anode sub-assembly comprising y anode layers each having anode layer thickness t_(y) and an anode layer peripheral edge extending toward the case side wall throughout a major length of said base peripheral edge, whereby each anode sub-assembly has an anode sub-assembly thickness T_(y) and further comprises an anode tab extending toward the case side wall in a minor portion of said case chamber periphery; and disposing a plurality of electrolyte bearing separator layers each having a separator peripheral edge extending toward the case side wall on each side of the anode sub-assembly and the cathode layer of the capacitor layer.
 21. The method of claim 19, wherein the number x anode layers is not equal to the number y anode layers.
 22. The method of claim 19, wherein the anode layer thickness t_(x) is equal to the anode layer thickness t_(y), and the number x anode layers is not equal to the number y anode layers.
 23. The method of claim 22, wherein the x anode layers comprise at least two anode layers and the y anode layers exceed the number of x anode layers.
 24. The method of claim 19, wherein the anode layer thickness t_(x) is not equal to the anode layer thickness t_(y), and the number x anode layers is not equal to the number y anode layers.
 25. The method of claim 19, wherein the anode layer thickness t₁ is not equal to the anode layer thickness t_(y), and the number x anode layers is equal to the number y anode layers.
 26. The method of claim 19, wherein certain or all of the x anode layers have differing anode layer thicknesses t_(x1), t_(x2), et seq., and certain or all of the y anode layers have differing anode layer thicknesses t_(y1), t_(y2), et seq., wherein t_(x1)≠t_(y1), t_(x2)≠t_(y2), et seq., and therefore either condition x≠y or x=y is sufficient in order to achieve differing anode sub-assembly thicknesses T_(x) and T_(y).
 27. The method of claim 19, wherein certain or all of the x anode layers have differing anode layer thicknesses t_(x1), t_(x2), et seq., and certain or all of the y anode layers have differing anode layer thicknesses t_(y1), t_(y2), et seq., wherein t_(x1)=t_(y1), t_(x2)=t_(y2), et seq., and therefore the condition x≠y is necessary in order to achieve differing anode sub-assembly thicknesses T_(x) and T_(y).
 28. A method of assembling an electrolytic capacitor comprising: providing a sealed capacitor case defining an interior case chamber, the case having a base having a base peripheral edge, a case side wall extending between the base peripheral edge through a side wall height to a side wall opening edge defining a case opening edge and a case chamber height H_(cw); providing a cover adapted to be sealed against the case opening edge to enclose the interior case chamber, whereby the interior case chamber has a case chamber periphery defined by said case side wall; forming an electrode stack assembly adapted to be located within the interior case chamber, the electrode stack assembly having a stack periphery configured in mating relation with the case chamber periphery and further comprising a plurality of N capacitor layers stacked in registration upon one another and between the case base and the cover through a stack height H_(N) selected to be equal to or less than the case chamber height H_(cw) by a predetermined tolerance, wherein N₁ capacitor layers of the N capacitor layers each have a first capacitor layer thickness T_(CL1) and N₂ capacitor layers of the N capacitor layers each have a second capacitor layer thickness T_(CL2), whereby the stack height H_(N) is dependent upon N₁*T_(CL1)+N₂*T_(CL2); disposing the electrode stack assembly within the interior case chamber; and hermetically sealing the case cover to the side wall opening edge;
 29. The method of claim 28 wherein the step of forming an electrode stack assembly further comprises: forming the N₁ capacitor layers each having a first capacitor layer thickness T_(CL1) by: forming a cathode layer having a cathode layer thickness and a cathode peripheral edge extending toward the case side wall throughout a major portion of said case chamber periphery and having a cathode tab extending toward the case side wall in a minor portion of said case chamber periphery; forming an anode sub-assembly comprising x anode layers each having anode layer thickness t_(x) and an anode layer peripheral edge extending toward the case side wall throughout a major length of said base peripheral edge, whereby each anode sub-assembly has an anode sub-assembly thickness T_(x) and further comprises an anode tab extending toward the case side wall in a minor portion of said case chamber periphery; and disposing a plurality of electrolyte bearing separator layers each having a separator peripheral edge extending toward the case side wall on each side of the anode sub-assembly and the cathode layer of the capacitor layer; and forming the N₂ capacitor layers each having a first capacitor layer thickness T_(CL2) by: forming a cathode layer having a cathode layer thickness and a cathode peripheral edge extending toward the case side wall throughout a major portion of said case chamber periphery and having a cathode tab extending toward the case side wall in a minor portion of said case chamber periphery; forming an anode sub-assembly comprising y anode layers each having anode layer thickness t_(y) and an anode layer peripheral edge extending toward the case side wall throughout a major length of said base peripheral edge, whereby each anode sub-assembly has an anode sub-assembly thickness T_(y) and further comprises an anode tab extending toward the case side wall in a minor portion of said case chamber periphery; and disposing a plurality of electrolyte bearing separator layers each having a separator peripheral edge extending toward the case side wall on each side of the anode sub-assembly and the cathode layer of the capacitor layer.
 30. The method of claim 28, wherein the number x anode layers is not equal to the number y anode layers.
 31. The method of claim 28, wherein the anode layer thickness t_(x) is equal to the anode layer thickness t_(y), and the number x anode layers is not equal to the number y anode layers.
 32. The method of claim 31, wherein the x anode layers comprise at least two anode layers and the y anode layers exceed the number of x anode layers.
 33. The method of claim 28, wherein the anode layer thickness t_(x) is not equal to the anode layer thickness t_(y), and the number x anode layers is not equal to the number y anode layers.
 34. The method of claim 28, wherein the anode layer thickness t_(x) is not equal to the anode layer thickness t_(y), and the number x anode layers is equal to the number y anode layers.
 35. The method of claim 28, wherein certain or all of the x anode layers have differing anode layer thicknesses t_(x1), t_(x2), et seq., and certain or all of the y anode layers have differing anode layer thicknesses t_(y1), t_(y2), et seq., wherein t_(x1)≠t_(y1), t_(x2)≠t_(y2), et seq., and therefore either condition x≠y or x=y is sufficient in order to achieve differing anode sub-assembly thicknesses T_(x) and T_(y).
 36. The method of claim 28, wherein certain or all of the x anode layers have differing anode layer thicknesses t_(x1), t_(x2), et seq., and certain or all of the y anode layers have differing anode layer thicknesses t_(y1), t_(y2), et seq., wherein t_(x1)=t_(y1, t) _(x2)=t_(y2), et seq., and therefore the condition x≠y is necessary in order to achieve differing anode sub-assembly thicknesses T_(x) and T_(y). 